Partially surface-mediated lithium ion-exchanging cells and method for operating same

ABSTRACT

A lithium super-battery cell comprising: (a) A cathode comprising a cathode active material having a surface area to capture or store lithium thereon, wherein the cathode active material is not a functionalized material and does not bear a functional group; (b) An anode comprising an anode current collector; (c) A porous separator disposed between the two electrodes; (d) A lithium-containing electrolyte in physical contact with the two electrodes, wherein the cathode active material has a specific surface area of no less than 100 m 2 /g being in direct physical contact with the electrolyte to receive lithium ions therefrom or to provide lithium ions thereto; and (e) A lithium source implemented at one or both of the two electrodes prior to a first charge or a first discharge cycle of the cell. This new generation of energy storage device exhibits the best properties of both the lithium ion battery and the supercapacitor.

This application claims the benefits of the following US patentapplications:

-   -   (a) C. G. Liu, David Neff, Zhenning Yu, Aruna Zhamu, and Bor Z.        Jang, “Lithium Super-battery with a Functionalized Nano Graphene        Cathode,” U.S. patent application Ser. No. 12/806,679 (Aug. 19,        2010)    -   (b) C. G. Liu, David Neff, Aruna Zhamu, and Bor Z. Jang,        “Lithium Super-battery with a Functionalized Disordered Carbon        Cathode,” U.S. patent application Ser. No. 12/924,211 (Sep. 23,        2010).    -   (c) Aruna Zhamu, C. G. Liu, David Neff, and Bor Z. Jang,        “Surface-Controlled Lithium Ion-Exchanging Energy Storage        Device,” U.S. patent application Ser. No. 12/928,927 (Dec. 23,        2010).    -   (d) Aruna Zhamu, C. G. Liu, David Neff, Z. Yu, and Bor Z. Jang,        “Partially and Fully Surface-Enabled Metal Ion-Exchanging        Battery Device,” U.S. patent application Ser. No. 12/930,294        (Jan. 3, 2011).    -   (e) A co-pending application, entitled “Surface-Mediated Lithium        Ion-Exchanging Energy Storage Device,” (A. Zhamu, et al),        concurrently submitted to the USPTO.

This invention is based on the research results of a project sponsoredby the US National Institute of Standard and Technology (NIST)Technology Innovation Program (TIP).

FIELD OF THE INVENTION

The present invention relates generally to the field of electrochemicalenergy storage devices and, more particularly, to a new lithiumion-exchanging energy storage device wherein the cathode does notinvolve lithium diffusion in and out of the bulk of a solidelectrode-active material (i.e., requiring no lithium intercalation orde-intercalation). The lithium storage mechanism in the cathode issurface-controlled, obviating the need for solid-state diffusion(intercalation or de-intercalation) of lithium, which otherwise is veryslow. This device has the high energy density of a lithium-ion batteryand the high power density of a supercapacitor (usually even higher thanthe power densities of supercapacitors). This device is herein referredto as a partially surface-mediated lithium ion-exchanging cell or alithium super-battery.

BACKGROUND OF THE INVENTION Supercapacitors (Ultra-Capacitors orElectro-Chemical Capacitors):

Supercapacitors are being considered for electric vehicle (EV),renewable energy storage, and modern grid applications. The highvolumetric capacitance density of a supercapacitor derives from usingporous electrodes to create a large surface area conducive to theformation of diffuse double layer charges. This electric double layer(EDL) is formed in the electrolyte near the electrode surface whenvoltage is imposed (FIGS. 1(B) and 2(A)). The required ions for this EDLmechanism near an electrode are pre-existing in the liquid electrolytewhen the cell is made or in a discharged state (FIG. 2(B)), and do notcome from the opposite electrode surface or interior. In other words,the required ions to be formed into an EDL near the surface of anegative electrode (anode) active material (e.g., activated carbonparticle) do not come from the bulk or surface per se of the positiveelectrode (cathode). The required ions (for the anode EDL formationduring the cell charging step) are not captured or stored earlier in thesurface or interior of a cathode active material (instead, they arepresent inside the electrolyte phase at either the anode side or thecathode side). Similarly, the required ions to be formed into an EDLnear the surface (but not on the surface) of a cathode active materialdo not come from the very surface or interior of an anode activematerial. Furthermore, the number of cations and the number of anionsthat participate in the charge storage function are essentially equal ina supercapacitor.

When the supercapacitor is re-charged, the ions (both cations andanions) that are already in the liquid electrolyte are electrochemicallydriven to form EDLs near their respective electrodes. There is no majorexchange of ions between an anode active material and a cathode activematerial. The amount (capacitance) of charges that can be stored isdictated solely by the concentrations of cations and anions that arealready available in the electrolyte. These concentrations are typicallyvery low (limited by the solubility of a salt in a solvent), resultingin a low energy density. Further, lithium ions are usually not part ofpreferred or commonly used supercapacitor electrolytes. When thesupercapacitor is discharged, both the cations and the anions are simplyre-distributed in the electrolyte in a random manner (FIG. 2(B)).

In some supercapacitors, the stored energy is further augmented bypseudo-capacitance effects due to some electrochemical reactions (e.g.,redox). In such a pseudo-capacitor, the ions involved in a redox pairalso pre-exist in the electrolyte. Again, there is no major exchange ofions between an anode active material and a cathode active material.

Since the formation of EDLs does not involve a chemical reaction or anexchange of ions between the two opposite electrodes, the charge ordischarge process of an EDL supercapacitor can be very fast, typicallyin seconds, resulting in a very high power density (typically3,000-8,000 W/Kg). Compared with batteries, supercapacitors offer ahigher power density, require no maintenance, offer a much highercycle-life, require a very simple charging circuit, and are generallymuch safer. Physical, rather than chemical, energy storage is the keyreason for their safe operation and extraordinarily high cycle-life.

Despite the positive attributes of supercapacitors, there are severaltechnological barriers to widespread implementation of supercapacitorsfor various industrial applications. For instance, supercapacitorspossess very low energy densities when compared to batteries (e.g., 5-8Wh/kg for commercial supercapacitors vs. 10-30 Wh/Kg for the lead acidbattery and 50-100 Wh/kg for the NiMH battery). Lithium-ion batteriespossess a much higher energy density, typically in the range of 100-180Wh/kg, based on the cell weight.

Lithium-Ion Batteries:

Although possessing a much higher energy density, lithium-ion batteriesdeliver a very low power density (typically 100-500 W/Kg), requiringtypically hours for re-charge. Conventional lithium-ion batteries alsopose some safety concern.

The low power density or long re-charge time of a lithium ion battery isdue to the mechanism of shuttling lithium ions between the interior ofan anode and the interior of a cathode, which requires lithium ions toenter or intercalate into the bulk of anode active material particlesduring re-charge, and into the bulk of cathode active material particlesduring discharge. For instance, as illustrated in FIG. 1(A), in a mostcommonly used lithium-ion battery featuring graphite particles as ananode active material, lithium ions are required to diffuse into theinter-planar spaces of a graphite crystal at the anode during re-charge.Most of these lithium ions have to come all the way from the cathodeside by diffusing out of the bulk of a cathode active particle, throughthe pores of a solid separator (pores being filled with a liquidelectrolyte), and into the bulk of a graphite particle at the anode. Theliquid electrolyte (where lithium ions can easily swim through) isexcluded from the bulk of a particle and, hence, the migration oflithium ions from the particle surface to the interior (e.g. the centerof a solid graphite particle) must occur via very slow solid-statediffusion (intercalation), as illustrated at the bottom portion of FIG.1(A).

During discharge, lithium ions diffuse out of the anode active material(e.g. de-intercalate out of graphite particles), migrate through theliquid electrolyte phase, and then diffuse into the bulk of complexcathode crystals (e.g. intercalate into particles lithium cobalt oxide,lithium iron phosphate, or other lithium insertion compound). In otherwords, liquid electrolyte only reaches the external surface of a solidparticle (e.g. graphite particle 10 μm in diameter) and lithium ionsswimming in the liquid electrolyte can only migrate (via fastliquid-state diffusion) to the graphite surface. To penetrate into thebulk of a solid graphite particle would require a slow solid-statediffusion (commonly referred to as “intercalation”) of lithium ions. Thediffusion coefficients of lithium in solid particles of lithium metaloxide are typically 10⁻¹⁶-10⁻⁸ cm²/sec (more typically 10⁻¹⁴-10⁻¹⁰cm²/sec), and those of lithium in liquid are approximately 10⁻⁶ cm²/sec.

In other words, these intercalation or solid-state diffusion processesrequire a long time to accomplish because solid-state diffusion (ordiffusion inside a solid) is difficult and slow. This is why, forinstance, the current lithium-ion battery for plug-in hybrid vehiclesrequires 2-7 hours of recharge time, as opposed to just seconds forsupercapacitors. The above discussion suggests that an energy storagedevice that is capable of storing as much energy as in a battery and yetcan be fully recharged in one or two minutes like a supercapacitor wouldbe considered a revolutionary advancement in energy storage technology.

More Recent Developments:

Recently, chemically functionalized, multi-walled carbon nano-tubes(CNTs) containing carbonyl groups were used by Lee, et al as a cathodematerial for a lithium-ion capacitor (LIC, as illustrated in FIG. 1(E))containing lithium titanate as the anode material [S. W. Lee, et al,“High Power Lithium Batteries from Functionalized Carbon Nanotubes,”Nature Nanotechnology, 5 (2010) 531-537]. In a super-batteryconfiguration (FIG. 1(D)), lithium foil was used as the anode andfunctionalized CNTs as the cathode, providing a relatively high powerdensity. However, the CNT-based electrodes prepared by thelayer-by-layer (LBL) approach suffer from several technical issuesbeyond just the high costs. Some of these issues are:

-   -   (1) CNTs contain a significant amount of impurity, particularly        those transition metal or noble metal particles used as a        catalyst required of a chemical vapor deposition process for CNT        production. These catalytic materials are highly undesirable in        a battery electrode due to their high propensity to cause        harmful reactions with electrolyte.    -   (2) CNTs tend to form a tangled mass resembling a hairball,        which is difficult to work with during electrode fabrication        (e.g., difficult to disperse in a liquid solvent or resin        matrix).    -   (3) The so-called “layer-by-layer” approach (LBL) used by Lee,        et al is a slow and expensive process that is not amenable to        large-scale fabrication of battery electrodes, or mass        production of electrodes with an adequate thickness (most of the        batteries have an electrode thickness of 100-300 μm). The        thickness of the LBL electrodes produced by Lee, et al (a noted        MIT research group) was limited to 3 μm or less.    -   (4) One might wonder how the thickness of the LBL CNT electrodes        would impact the performance of the cells. A careful inspection        of the data provided by Lee, et al (e.g. Fig. S-7 of the        Supporting Material of Lee, et al) show that the power density        dropped by one order of magnitude when the LBL CNT electrode        thickness was increased from 0.3 μm to 3.0 μm. The performance        is likely to drop even further if the electrode thickness is        increased to that of a useful battery or supercapacitor        electrode (e.g., 100-300 μm).    -   (5) Although the ultra-thin LBL CNT electrodes provide a high        power density (since Li ions only have to travel an extremely        short distance), there was no data to prove that CNT-based        electrodes of practical thickness could even work due to the        poor CNT dispersion and electrolyte inaccessibility issues. Lee,        et al showed that the CNT-based composite electrodes prepared        without using the LBL approach did not exhibit good performance.    -   (6) CNTs have very limited amounts of suitable sites to accept a        functional group without damaging the basal plane structure. A        CNT has only one end that is readily functionalizable and this        end is an extremely small proportion of the total CNT surface.        By chemically functionalizing the exterior basal plane, one        could dramatically compromise the electronic conductivity of a        CNT.

Most recently, our research groups have reported, in two patentapplications, the development of two new classes of highly conductingcathode active materials having a functional group that is capable ofrapidly and reversibly forming a redox reaction with lithium ions. Thesematerials are nano graphene (both single-layer graphene and multi-layergraphene sheets, collectively referred to as nano graphene platelets orNGPs) and disordered carbon (including soft carbon, hard carbon, carbonblack, activated carbon, amorphous carbon, etc). These two patentapplications are: C. G. Liu, et al., “Lithium Super-battery with aFunctionalized Nano Graphene Cathode,” U.S. patent application Ser. No.12/806,679 (Aug. 19, 2010) and C. G. Liu, et al, “Lithium Super-batterywith a Functionalized Disordered Carbon Cathode,” U.S. patentapplication Ser. No. 12/924,211 (Sep. 23, 2010).

These new types of cathode active materials (used in the so-called“lithium super-battery”) include a chemically functionalized nanographene platelet (NGP) or a functionalized disordered carbon materialhaving certain specific functional groups capable of reversibly andrapidly forming a redox pair with a lithium ion during the charge anddischarge cycles of a battery cell. In these two patent applications,the functionalized disordered carbon or functionalized NGP is used inthe cathode (not the anode) of the lithium super-battery. In thiscathode, lithium ions in the liquid electrolyte only have to migrate tothe edges or surfaces of graphene sheets (in the case of functionalizedNGP cathode), or the edges/surfaces of the aromatic ring structures(small graphene sheets) in a disordered carbon matrix. No solid-statediffusion is required at the cathode. The presence of a functionalizedgraphene or carbon having functional groups thereon enables reversiblestorage of lithium on the surfaces (including edges), not the bulk, ofthe cathode material. Such a cathode material provides one type oflithium-storing or lithium-capturing surface.

In conventional lithium-ion batteries, lithium ions must diffuse intoand out of the bulk of a cathode active material, such as lithium cobaltoxide (LiCoO₂) and lithium iron phosphate (LiFePO₄). In theseconventional lithium-ion batteries, lithium ions must also diffuse inand out of the inter-planar spaces in a graphite crystal serving as ananode active material. The lithium insertion or extraction procedures atboth the cathode and the anode are very slow. Due to these slowprocesses of lithium diffusion in and out of these intercalationcompounds (commonly referred to as solid-state diffusion orintercalation processes), the conventional lithium ion batteries do notexhibit a high power density and the batteries require a long re-chargetime. None of these conventional devices rely on select functionalgroups (e.g. attached at the edge or basal plane surfaces of a graphenesheet) that readily and reversibly form a redox reaction with a lithiumion from a lithium-containing electrolyte.

In contrast, the super-battery as reported in our two earlier patentapplications (U.S. application Ser. No. 12/806,679 and Ser. No.12/924,211), relies on the operation of a fast and reversible reactionbetween a functional group (attached or bonded to a graphene structureat the cathode) and a lithium ion in the electrolyte. Lithium ionscoming from the anode side through a separator only have to diffuse inthe liquid electrolyte to reach a surface/edge of a graphene plane inthe cathode. These lithium ions do not need to diffuse into or out ofthe volume of a solid particle. Since no diffusion-limited intercalationis involved at the cathode, this process is fast and can occur inseconds. Hence, this is a totally new class of hybridsupercapacitor-battery that exhibits unparalleled and unprecedentedcombined performance of an exceptional power density, high energydensity, long and stable cycle life, and wide operating temperaturerange. This device has the best of both battery and supercapacitorworlds.

In the lithium super-batteries described in these two earlier patentapplications, the anode comprises either particles of a lithiumtitanate-type anode active material (Type-2 super-battery, stillrequiring some solid state diffusion in the first discharge or firstcharge operation, but no intercalation thereafter) or a lithium foilalone, along with an anode current collector (Type-1 super-battery).Hence, these lithium super-batteries are also referred to as partiallysurface-mediated, lithium ion-exchanging cells.

The instant application claims the benefits of the two co-pending U.S.application Ser. No. 12/806,679 (Aug. 19, 2010) and Ser. No. 12/924,211(Sep. 23, 2010) Ser. No. 12/928,927, but discloses a more general andversatile approach that also involves the exchange of massive lithiumions between an anode and the surfaces of a cathode. These cathodesurfaces in the instant application are not based on a functionalizedmaterial (defined as a material bearing a functional group capable offorming a redox pair with lithium). Instead, we have most surprisinglyobserved that, without any functional group, some graphene surfaces arefully capable of capturing or trapping more lithium atoms. Regardless ifthe surfaces contain functional groups or not, graphene surfaces arecapable of storing lithium atoms in a stable and reversible manner,provided these surfaces are accessible to lithium ion-containingelectrolyte and are in direct contact with the electrolyte. Afterextensive in-depth studies, we have further observed that the lithiumstoring capacity is in direct proportion to the total surface area thatis directly exposed to the lithium ion-containing electrolyte. Forinstance, some of the specific capacity measurements were conducted onthe cells containing a pristine graphene cathode composed of essentiallyall carbon atoms only (>99% C), having no functional group such as —OHor —COOH. Hence, the mechanism of Li-functional group redox reactioncould not be the lithium storage mechanism. The two co-pending US patentapplications claim the functionalized material-based super-batteries,but the instant application claims the super-batteries based on anon-functionalized material cathode.

SUMMARY OF THE INVENTION

For the purpose of defining the scope of the claims in the instantapplication, the lithium super-battery or partially surface-mediatedcell does not include any lithium-air (lithium-oxygen) cell,lithium-sulfur cell, or any cell wherein the operation of the energystorage device involves the introduction of oxygen from outside of thedevice, or involves the formation of a metal oxide, metal sulfide, metalselenide, metal telluride, metal hydroxide, or metal-halogen compound atthe cathode. These cells involve a strong cathode reaction during celldischarge and, hence, the re-charge reaction is not very reversible(having very low round-trip efficiency) and exhibit extremely poor powerdensity.

The present invention provides a super-battery cell, comprising: (a) Apositive electrode (cathode) comprising a cathode active material havinga surface area to capture or store lithium thereon (the cathode activematerial is not a functionalized material, having no functional group tocapture a lithium atom); (b) A negative electrode (anode) comprising ananode current collector; (c) A porous separator disposed between the twoelectrodes; (d) A lithium-containing electrolyte in physical contactwith the two electrodes, wherein the cathode active material has aspecific surface area of no less than 100 m²/g being in direct physicalcontact with the electrolyte to receive lithium ions therefrom or toprovide lithium ions thereto; and (e) A lithium source implemented atthe anode or cathode prior to a first discharge or a first charge cycleof the cell. The lithium source may be preferably in a form of solidlithium foil, lithium chip, lithium powder, or surface-stabilizedlithium particles. Such a cell is herein referred to as a Type-1super-battery and the operation normally does not involve any solidstate diffusion. The lithium source may be a layer of lithium thin filmpre-loaded on surfaces of an anode active material.

If the lithium source is a lithium intercalation compound or a lithiatedcompound (such as prelithiated graphite, prelithiated carbon, lithiatedtitanium dioxide, lithium titanate, lithium manganate, a lithiumtransition metal oxide, or Li₄Ti₅O₁₂), such a cell is referred to as aType-2 super-battery. In a Type-2 super-battery, the first discharge orfirst charge operation can involve some de-intercalation or solid-statediffusion, but the subsequent charge/discharge cycles are essentiallyintercalation-free and de-intercalation-free (essentially involving nosolid-state diffusion).

The surfaces of a super-battery electrode material (e.g., pristinegraphene containing essentially >99% carbon), despite having nofunctional groups bonded thereon, are capable of capturing lithium ionsdirectly from a liquid electrolyte phase and storing lithium atoms onthe surfaces in a reversible and stable manner, even though thismono-layer of lithium atoms remains immersed in electrolyte.Scientifically this has been quite unexpected since one would expect theliquid electrolyte to be more competitive than bare graphene surfacesfor retaining or capturing lithium.

The electrolyte preferably comprises liquid electrolyte (e.g. organicliquid or ionic liquid) or gel electrolyte in which lithium ions have ahigh diffusion coefficient. Solid electrolyte is normally not desirable,but some thin layer of solid electrolyte may be used if it exhibits arelatively high diffusion rate.

To illustrate the operational principle of this new super-battery (FIG.3(A), Type-1), one may consider a case wherein a lithium source (e.g.small pieces of lithium foil) is implemented between an anode currentcollector and a porous polymer separator when the battery device ismade, and wherein a nano-structured cathode comprises non-functionalizedgraphene sheets surrounded by interconnected pores that are preferablymeso-scaled (2 nm-50 nm), but can be smaller than 2 nm. Referring toFIG. 3(A)-(C), during the first discharge cycle, lithium foil is ionizedto generate lithium ions in the liquid electrolyte. Lithium ions rapidlymigrate through the pores of the polymer separator into the cathodeside. Since the cathode is also meso-porous having interconnected poresto accommodate liquid electrolyte therein, lithium ions basically justhave to swim through liquid to reach an active site (not a functionalgroup) on a surface or edge of a graphene sheet at the cathode. Thegraphene surface is in direct contact with electrolyte and readilyaccepts lithium ions from the electrolyte. Because all the steps(lithium ionization, liquid phase diffusion, and surfacetrapping/adsorption/capturing) are fast and no solid-state diffusion isrequired, the whole process is very fast, enabling fast discharging ofthe cell and a high power density. This is in stark contrast to theconventional lithium-ion battery wherein lithium ions are required todiffuse into the bulk of a solid cathode particle (e.g., micron-sizedlithium cobalt oxide) during discharge, which is a very slow process.During discharge of the lithium-ion battery, these lithium ions have tocome out of the bulk of graphite particles at the anode. Since liquidelectrolytes only reaches the surfaces of these micron-scaled graphiteparticles (not in direct contact with the graphene surfaces inside thegraphite particle), the lithium de-intercalation step also require aslow solid-state diffusion.

In the above example, the discharge process continues until either thelithium foil is completely ionized or all the active sites on thecathode active materials are occupied by lithium atoms. Duringre-charge, lithium ions are released from the massive surfaces of thecathode active material (having no functional material attachedthereon), diffuse through liquid electrolyte, and get captured by thesurface of an anode current collector or a lithium source material.Again, no solid-state diffusion is required and, hence, the wholeprocess is very fast, requiring a short re-charge time. This is asopposed to the required solid-state diffusion of lithium ions into thebulk of graphite particles at the anode of a conventional lithium-ionbattery.

Clearly, the presently invented battery device provides a very uniqueplatform of exchanging lithium ions between an anode and the massivesurfaces of a cathode that requires no solid-state diffusion in bothelectrodes. The process is substantially dictated by the step ofsurface-capturing of lithium, plus the liquid-phase diffusion (all beingvery fast). Hence, the device is also herein referred to as a partiallysurface-mediated, lithium ion-exchanging battery. This is a totallydifferent and patently distinct class of energy storage device than theconventional lithium-ion battery, wherein solid-state diffusion oflithium (intercalation and de-intercalation) is required at both theanode and the cathode during both the charge and discharge cycles.

In some super-battery cells, the lithium source can be a lithiatedcompound (e.g. implemented at the anode or the cathode) or lithiumalloy. The lithium compound or lithium alloy is preferably a nano-scaledmaterial having at least one dimension (e.g. thickness or diameter) lessthan 100 nm (preferably less than 20 nm and most preferably less than 10nm).

This new partially surface-mediated, lithium ion-exchanging batterydevice is also patently distinct from the conventional supercapacitorbased on the electric double layer (EDL) mechanism or pseudo-capacitancemechanism. In both mechanisms, no lithium ions are exchanged between thetwo electrodes (since lithium is not stored in the bulk or surfaces ofthe electrode; instead, they are stored in the electric double layersnear the electrode surfaces, but in the electrolyte). When asupercapacitor is re-charged, the electric double layers are formed nearthe activated carbon surfaces at both the anode and the cathode sides.When the supercapacitor is discharged, both the negatively chargedspecies and the positively charged species get randomized in theelectrolyte (staying further away from electrode material surfaces). Incontrast, when a super-battery is re-charged, essentially all of thelithium ions are electro-plated onto the surfaces of the anode currentcollector and the cathode side is essentially lithium-free. When thesuper-battery is discharged, essentially all the lithium ions arecaptured by the cathode active material surfaces (stored in the defectsor bonded to the benzene ring centers). Very few lithium ions stay inthe electrolyte.

More significantly, all the prior art supercapacitors do not contain anextra lithium source and their operations do not involve ionization oflithium from this lithium source. The charge storage capacitance of asupercapacitor (even when using a Li-containing electrolyte) is limitedby the amounts of cations and anions that participate in the formationof EDL charges. These amounts are dictated by the original concentrationof Li⁺ ions and their counter ions (anions) from a lithium salt, whichare in turn dictated by the solubility limits of these ions in theelectrolyte solvent. To illustrate this point, let us assume that onlyup to 1 mole of Li⁺ ions can be dissolved in 1 mL of a solvent and thereare totally 5 mL of solvent added to a particular supercapacitor cell,Then, there is a maximum of 5 moles of Li⁺ ions that can be present inthe total cell and this amount dictates the maximum amount of chargesthat can be stored in this supercapacitor.

In contrast (and quite surprisingly), the amounts of lithium ions thatcan be shuttled between the anode surface and the cathode surface of asuper-battery are not limited by the chemical solubility of lithium saltin this same solvent. Assume that an identical 5 mL of solvent(containing 5 moles of Li⁺ ions, as described above for asupercapacitor) is used in the super-battery. Since the solvent isalready fully saturated with the lithium salt, one would expect thatthis solvent cannot and will not accept any more Li⁺ ions from an extralithium source (5 moles being the maximum). Consequently, one wouldexpect that these 5 moles of Li⁺ ions are the maximum amount of lithiumthat we can use to store charges (i.e., the maximum amount of Li⁺ ionsthat can be captured by the cathode during discharge, or the maximumamount of Li⁺ ions that can be captured by the anode during re-charge).Contrary to this expectation by a person of ordinary or evenextra-ordinary skill in the art of electrochemistry, we havesurprisingly discovered that the amount of Li⁺ ions that can be capturedby the surfaces of either electrode (or, the amount of Li⁺ ions that canbe shuttled between the two electrodes) in a super-battery typically farexceeds this solubility limit by 1 or 2 orders of magnitude. Theimplementation of a lithium source at the anode appears to have defiedthis expectation by providing dramatically more lithium ions than whatthe solvent can dissolve therein.

Further surprisingly, in a super-battery, the amount of lithium capableof contributing to the charge storage is controlled (limited) by theamount of surface active sites of a cathode capable of capturing lithiumions from the electrolyte. This is so even when this amount of surfaceactive sites far exceeds the amount of Li⁺ ions that the solvent canhold at one time (e.g. 5 moles in the present discussion), provided thatthe implemented lithium source can provide the extra amount lithiumions. These active sites can be just the surface defects of graphene, orthe benzene ring centers on a graphene plane (FIGS. 4(D) and (E)). Alsoquite unexpectedly, lithium atoms are found to be capable of stronglyand reversibly bonding to the individual centers of benzene rings(hexagons of carbon atoms) that constitute a graphene sheet, or of beingreversibly trapped by graphene surface defect sites.

In this super-battery, the cathode active material is not afunctionalized material (i.e., having no functional group attached toits surface that is exposed to electrolyte). The functionalized materialmeans a material having a functional group (e.g., carbonyl) that iscapable of reacting with a lithium atom or ion to form a redox pair.However, it is essential that the cathode active material has a highspecific surface area (>100 m²/g) that is in direct contact with theelectrolyte (e.g. being directly immersed in electrolyte) and capable ofcapturing lithium ions from the electrolyte and storing the lithiumatoms in the surface active sites (e.g. surface defects and benzene ringcenters). Preferably, the cathode active material has a specific surfacearea no less than 500 m²/gram (preferably >1,000 m²/gram, morepreferably >1,500 m²/gram, and most preferably >2,000 m²/gram) to storeor support lithium ions or atoms thereon.

Preferably, the lithium source comprises a lithium chip, lithium foil,lithium powder, surface-passivated or stabilized lithium particles, or acombination thereof. The lithium source may be implemented at the anodeside before the first discharge procedure is carried out on this batterydevice. Alternatively, the lithium source may be implemented at thecathode side before the first charge procedure is carried out on thisbattery device. As another alternative, both the cathode and the anodemay be fabricated to contain some lithium source during the batterymanufacturing process. It is important to note that this solid lithiumsource provides the majority of the lithium ions that are to beexchanged between the anode surfaces and the cathode surfaces during thecharge-discharge cycles. Although the lithium-containing electrolytenaturally provides some of the needed lithium ions, this amount is waytoo short to enable the battery device to deliver a high energy density.This is why any symmetric supercapacitor, even if containing Li-basedelectrolyte, does not exhibit a high energy density.

Preferably, the non-functionalized cathode active material is selectedfrom the following: (a) A porous disordered carbon material selectedfrom a soft carbon, hard carbon, polymeric carbon or carbonized resin,meso-phase carbon, coke, carbonized pitch, carbon black, activatedcarbon, or partially graphitized carbon; (b) A graphene materialselected from a single-layer sheet or multi-layer platelet of graphene,graphene oxide, graphene fluoride, hydrogenated graphene, nitrogenatedgraphene, boron-doped graphene, nitrogen-doped graphene, or chemicallyor thermally reduced graphene oxide; (c) Exfoliated graphite; (d)Meso-porous carbon (e.g. obtained by template-assisted synthesis orchemical activation of meso-phase carbon); (e) A carbon nanotubeselected from a single-walled carbon nanotube or multi-walled carbonnanotube; (f) A carbon nano-fiber, metal nano-wire, metal oxidenano-wire or fiber, or conductive polymer nano-fiber, or (g) Acombination thereof.

Although non-functionalized CNTs are not preferred nano-structuredmaterials due to the high costs and other technical issues, CNTs (aloneor in combination with another nano-structured material) can still beused in the presently invented partially surface-controlled lithiumion-exchanging battery. This can include a non-functionalizedsingle-walled or multi-walled carbon nanotube (CNT), slightly oxidizedCNT, fluorinated CNT, hydrogenated CNT, nitrogenated CNT, boron-dopedCNT, nitrogen-doped CNT, or doped CNT. The nano-structured cathodematerial may include non-functionalized nano graphene, carbon nanotube,disordered carbon, or nano graphite, may simply provide a surface uponwhich lithium atoms can be deposited, e.g. via defect site trapping orbenzene ring center capturing. The mere existence of a nano-structuredmaterial, even without a reactive functional group, can still provide ahuge amount of lithium-storing surfaces. This non-functionalized surfaceis the lithium-storing surface in the present application.

The disordered carbon material may be formed of two phases with a firstphase being graphite crystals or stacks of graphene planes and a secondphase being non-crystalline carbon and wherein the first phase isdispersed in the second phase or bonded by the second phase. Thedisordered carbon material may contain less than 90% by volume ofgraphite crystals and at least 10% by volume of non-crystalline carbon.

The lithium source may be selected from lithium metal (e.g., in a thinfoil or powder form, preferably stabilized or surface-passivated), alithium metal alloy, a mixture of lithium metal or lithium alloy with alithium intercalation compound, a lithiated compound, lithiated titaniumdioxide, lithium titanate, lithium manganate, a lithium transition metaloxide, Li₄Ti₅O₁₂, or a combination thereof. Specifically, the lithiumintercalation compound or lithiated compound may be selected from thefollowing groups of materials: (a) Lithiated silicon (Si), germanium(Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi), zinc (Zn),aluminum (Al), titanium (Ti), cobalt (Co), nickel (Ni), manganese (Mn),cadmium (Cd), and mixtures thereof; (b) Lithiated alloys orintermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Co, Ni,Mn, Cd, and their mixtures; (c) Lithiated oxides, carbides, nitrides,sulfides, phosphides, selenides, tellurides, or antimonides of Si, Ge,Sn, Pb, Sb, Bi, Zn, Al, Fe, Ti, Co, Ni, Mn, Cd, and mixtures orcomposites thereof; (d) Lithiated salts or hydroxides of Sn; and (e)Prelithiated graphite or prelithiated carbon material.

The electrolyte may be preferably selected from any of the electrolytesused in conventional lithium ion batteries or lithium metal batteries.The electrolyte is preferably liquid electrolyte or gel electrolyte. Theelectrolyte is preferably an organic electrolyte or a lithium salt-dopedionic liquid. In the battery device, the positive electrode preferablyhas a thickness greater than 5 μm, preferably greater than 50 μm, andmore preferably greater than 100 μm.

In a preferred embodiment, in the super-battery, at least 90% of thelithium is stored on surfaces of the anode current collector when thedevice is in a charged state, or at least 90% of the lithium is storedon surfaces of the cathode active material (lithium being captured bycathode surfaces) when the device is in a discharged state.

The super-battery typically operates in a voltage range of from 1.0volts to 4.5 volts, but can be prescribed to operate in a subset of thisrange (e.g. from 1.5 volts to 4.0 volts or from 2.0 volts to 3.9 volts,etc). It is also possible to operate above 4.5 volts, or slightly below1.0 volts (although not preferred). It may be noted that a symmetricsupercapacitor featuring an organic electrolyte can only operate up to3.0 volts and typically operates from 0 to 2.7 volts. In contrast, asuper-battery using exactly the same organic electrolyte typicallyoperates from 1.5 volts to 4.5 volts. This is another piece of evidencethat the super-battery and the supercapacitor are two fundamentallydistinct classes of energy storage devices, operating on differentmechanisms and principles.

It may be further noted that the open-circuit voltage of an EDLCsupercapacitor is essentially zero volts when the cell is made andtested for the first time. In contrast, the open-circuit voltage of asuper-battery is typically in the range of 1.0 volts-2.0 volts.

Preferably, the charge and/or discharge operation of the super-batterydoes not involve lithium intercalation or solid state diffusion. This isusually the case even if multi-layer graphene platelets are used in thecathode. Lithium intercalation into interstitial spaces between twographene planes typically occur in a voltage below 1.5 volts (relativeto Li/Li⁺), mostly below 0.5 volts. The presently invented lithiumion-exchanging cell involves shuttling lithium ions between the surfacesof an anode current collector and surfaces of a cathode, which operateson the range of 1.5 volts to 4.5 volts.

Quite surprisingly, the super-battery provides an energy densitytypically of no less than 150 Wh/kg and power density no lower than 25Kw/kg, all based on the total electrode weight. More typically, thebattery device provides an energy density of greater than 300 Wh/kg andpower density greater than 20 Kw/kg. In many cases, the battery deviceprovides an energy density greater than 400 Wh/kg and power densitygreater than 10 Kw/kg. Most typically, the battery device provides anenergy density greater than 300 Wh/kg or a power density greater than100 Kw/kg. In some cases, the power density is significantly higher than200 Kw/kg, or even higher than 400 Kw/kg, which is 1-3 orders ofmagnitude higher than the power densities (1-10 Kw/kg) of conventionalsupercapacitors.

In the presently invented super-battery, the positive electrodepreferably has a thickness greater than 5 μm, more preferably greaterthan 50 μm, and most preferably greater than 100 μm.

The present invention also provides a method of operating a partiallysurface-mediated, lithium ion-exchanging cell (also referred to as asuper-battery cell). The method includes implementing a lithium sourceat the anode and ionizing the lithium source to release lithium ionsinto the electrolyte during the first discharge cycle of the device. Themethod further includes electrochemically driving the released lithiumions onto the cathode where the released lithium ions are captured bythe cathode active material surfaces. The method can further include astep of releasing lithium ions from the cathode surfaces during are-charge cycle of the device, electrically driving the released lithiumions to the anode current collector surface using an external batterycharging device.

Alternatively, the method may include implementing a lithium source atthe cathode and operating the lithium source to release lithium ionsinto the electrolyte during the first charge cycle of the device.

The invention further provides a method of operating a partiallysurface-mediated energy storage device, which method includes: (A)Providing a partially surface-mediated cell comprising an anode, alithium source, a porous separator, liquid or gel electrolyte, and acathode, wherein the cathode has a non-functionalized material havinglithium-capturing surfaces; (B) Releasing lithium ions from the lithiumsource during the first discharge of the device; (C) Exchanging lithiumions between an anode current collector surface and thelithium-capturing surfaces of the cathode during a subsequent charge ordischarge. Preferably, both the charge and discharge of the device donot involve lithium intercalation or solid state diffusion.

The instant application discloses another method of operating apartially surface-mediated energy storage device. The method includes:(A) Providing a partially surface-mediated cell comprising an anodecurrent collector, a lithium source, a porous separator, electrolyte(having an initial amount of lithium ions), and a cathode, wherein thecathode has a material having lithium-capturing surfaces in contact withthe electrolyte; (B) Releasing lithium ions from the lithium source intothe electrolyte during the first discharge of this device; (C) Operatingthe cathode to capture lithium ions from the electrolyte and store thecaptured lithium on cathode surfaces (preferably having a specificsurface area of greater than 100 m²/g, more preferably greater than1,000 m²/g, and most preferably greater than 2,000 m²/g); and (D)Exchanging an amount of lithium ions (greater than the initial amount)between the anode current collector and the lithium-capturing surfacesof the cathode during a subsequent charge or discharge operation,wherein the charge operation involves no lithium intercalation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 (A) a prior art lithium-ion battery cell using graphite as ananode active material and lithium iron phosphate (or lithium cobaltoxide, etc) as a cathode active material; (B) a prior art EDLsupercapacitor; (C) a prior art lithium-ion capacitor (LIC) with aprelithiated graphite anode and an activated carbon cathode; (D) a priorart lithium super-battery cell with a lithium foil anode and a cathodemade of functionalized CNT; (E) a prior art lithium-ion capacitor with alithium titanate as an anode active material and a cathode made of afunctionalized CNT.

FIGS. 2 (A) and (B) are for illustrating the charged and dischargedstate, respectively, of a prior art EDL supercapacitor; and (C) and (D)are for illustrating the charged and discharged state, respectively, ofa prior art lithium-ion capacitor (LIC).

FIG. 3 (A) The structure of a super-battery cell when it is made (priorto the first discharge or charge cycle), containing an anode currentcollector, a lithium source (e.g. lithium foil or surface-stabilizedlithium powder), a porous separator, liquid electrolyte, anano-structured non-functionalized material at the cathode; (B) Thestructure of this device after its first discharge operation (lithium isionized with the lithium ions diffusing through liquid electrolyte toreach the surfaces of nano-structured cathode and get rapidly capturedby these surfaces); (C) The structure of this battery device after beingre-charged (lithium ions are released from the cathode surfaces,diffusing through liquid electrolyte to reach the anode side and getrapidly plated onto the surface of the anode current collector or thesurface of a layer of lithium).

FIG. 4 (A) Schematic of a lithium storage mechanism disclosed in aco-pending application (the functional group attached to an edge orsurface of an aromatic ring or small graphene sheet can readily reactwith a lithium ion to form a redox pair); (B) Possible formation ofelectric double layers as a minor or negligible mechanism of chargestorage; (C) A major lithium storage mechanism (lithium captured at abenzene ring center of a graphene plane), which is fast, reversible, andstable; (D) Another major lithium storage mechanism (lithium atomstrapped in a graphene surface defect).

FIG. 5 The electrochemical potential of the anode, the cathode, and thecell for (A) a symmetric supercapacitor (EDLC) and (B) alithium-capacitor during a charge and discharge cycle.

FIG. 6 (A) A SEM image of curved nano graphene sheets; (B) A SEM imageof another graphene morphology. All these graphene morphologies providevery high specific surface area (typically from 300 to 2,000 m²/g).

FIG. 7 (A) Ragone plots of 4 cells: a functionalized disorderedcarbon-based lithium super-battery, a corresponding non-functionalizedlithium super-battery, a prior art symmetric supercapacitor, and anotherprior art symmetric supercapacitor based on LBL functionalized CNTelectrodes (Lee, et al); (B) Lon-term cycling stability of anon-functionalized NGP-based super-battery of the instant applicationvs. that of a super-battery (with functional groups in its cathode) ofan earlier application.

FIG. 8 (A) Ragone plots of a functionalized NGP-based lithiumsuper-battery and a corresponding non-functionalized lithiumsuper-battery; (B) Lon-term cycling stability of a non-functionalizedNGP-based super-battery of the instant application vs. that of asuper-battery (with functional groups in its cathode) of an earlierapplication.

FIG. 9 The Ragone plots of a Type-2 lithium-super-battery featuring aprelithiated graphite as a lithium-ion source and a graphene-basedcathode active material (with an open-circuit voltage of 1.5 volts andoperating in the voltage range of 1.5-4.5 volts) and a correspondinglithium-ion capacitor using a prelithiated graphite as an anode activematerial and an activated carbon cathode (with an open-circuit voltageof 2.2 volts and operating in the voltage range of 2.2-3.8 volts). Theselection of a graphene cathode as opposed to an activated carboncathode (hence, different in composition) makes a major difference inperformance between a Type-2 lithium battery of the instant inventionand the prior art lithium-ion capacitor. The operating modes are alsodifferent.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention may be more readily understood by reference to thefollowing detailed description of the invention taken in connection withthe accompanying drawing figures, which form a part of this disclosure.It is to be understood that this invention is not limited to thespecific devices, methods, conditions or parameters described and/orshown herein, and that the terminology used herein is for the purpose ofdescribing particular embodiments by way of example only and is notintended to be limiting the claimed invention.

This invention provides an electrochemical energy storage device that isherein referred to as a partially surface-mediated, lithiumion-exchanging cell (or a super-battery). This super-battery deviceexhibits a power density significantly higher than the power densitiesof conventional supercapacitors and dramatically higher than those ofconventional lithium ion batteries. This device exhibits an energydensity comparable to that of a battery, and significantly higher thanthose of conventional supercapacitors.

This super-battery is composed of a positive electrode containing anon-functionalized material having a lithium-storing orlithium-capturing surface (the non-functionalized material beingpreferably nano-structured with nano-scaled or meso-scaled pores andgreat amounts of surface areas containing no chemical functional group,such as —NH₂ or —COOH, to form a redox pair with a lithium), a negativeelectrode containing an anode current collector, a porous separatordisposed between the two electrodes, a lithium-containing electrolyte inphysical contact with the two electrodes, and a lithium ion sourceimplemented at the anode or the cathode. The lithium-capturing surfaceis in direct contact with electrolyte to capture lithium ions therefromor to release lithium ions thereto. Preferred electrolyte types includeorganic liquid electrolyte, gel electrolyte, and ionic liquidelectrolyte (preferably containing lithium ions), or a combinationthereof, although one may choose to use aqueous or solid electrolytes.

The lithium ion source can be selected from a lithium chip, lithiumfoil, lithium powder, surface stabilized lithium particles, lithium filmcoated on a surface of an anode or cathode active material, or acombination thereof. In one preferred embodiment, the anode currentcollector is prelithiated, or pre-coated or pre-plated with lithium. Inaddition to relatively pure lithium metal, the lithium source may beselected from a lithium metal alloy, a mixture of lithium metal orlithium alloy with a lithium intercalation compound, a lithiatedcompound, lithiated titanium dioxide, lithium titanate, lithiummanganate, a lithium transition metal oxide, Li₄Ti₅O₁₂, or a combinationthereof. The lithium intercalation compound or lithiated compound may beselected from the following groups of materials: (a) Lithiated silicon(Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), bismuth (Bi),zinc (Zn), aluminum (Al), titanium (Ti), cobalt (Co), nickel (Ni),manganese (Mn), cadmium (Cd), and mixtures thereof; (b) Lithiated alloysor intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Co,Ni, Mn, Cd, and their mixtures; (c) Lithiated oxides, carbides,nitrides, sulfides, phosphides, selenides, tellurides, or antimonides ofSi, Ge, Sn, Pb, Sb, Bi, Zn, Al, Fe, Ti, Co, Ni, Mn, Cd, and mixtures orcomposites thereof, or (d) Lithiated salts or hydroxides of Sn.

Although there is no limitation on the electrode thickness, thepresently invented positive electrode preferably has a thickness greaterthan 5 μm, more preferably greater than 50 μm, and most preferablygreater than 100 μm. An example of such a partially surface-mediated,ion-exchanging battery device is given in FIG. 3.

Theoretical Aspects (Lithium Ion Diffusion Kinetics of ConventionalLithium-Ion Batteries, Lithium-Ion Capacitors, and Super-Batteries)

Not wishing to be constrained by any theory, but we would like to offerthe following theoretical considerations that perhaps are helpful to thereaders. We will provide some insight as to how a partiallysurface-mediated energy storage device operates and why such a lithiumion-exchanging battery exhibits exceptional power densities un-matchedby conventional supercapacitors. We will also shed some light on why theelectrode thickness of a lithium cell (including the partiallysurface-mediated lithium super-battery and conventional lithium-ionbattery) plays such a critical role in dictating the power density insuch a dramatic manner.

The internal structure of a conventional lithium-ion battery may beschematically shown in FIG. 1(A). In a battery discharge situation,lithium ions must diffuse (de-intercalate) out from the bulk of an anodeactive material particle, such as graphite, silicon, and lithiumtitanate (particle diameter=d_(a) and the average solid-state diffusiondistance=d_(a)/2), and then migrate in liquid electrolyte across theanode thickness (anode layer thickness=La and the average diffusiondistance=La/2). Subsequently, lithium ions must move (in liquidelectrolyte) across a porous separator (thickness=Ls), diffuse acrosspart of the cathode thickness (thickness=Lc) in liquid electrolyte toreach a particular cathode active material particle (average diffusiondistance=Lc/2), and then diffuse into (intercalate) the bulk of aparticle (diameter=d_(c) and the average solid-state diffusion distancerequired=d_(c)/2). In a re-charge situation, the lithium ions move inthe opposite direction, but must travel approximately the samedistances.

In other words, the operation of a conventional lithium-ion batteryinvolves de-intercalation of lithium ions from the bulk (not thesurface) of an electrode active material particle in one electrode(e.g., anode, during discharge) and intercalation of lithium ions intothe bulk of an electrode active material particle in the oppositeelectrode (e.g. cathode). In general, diffusion through a liquidelectrolyte is fast, but diffusion through a solid is dramaticallyslower (by 3-8 orders of magnitude). The presently invented partiallysurface-mediated cell operates essentially on the exchange of massivelithium ions between the anode current collector surface and surfaces ofthe nano-structured cathode (and not in the bulk of the electrode, as inlithium-ion batteries). This strategy completely removes the need forthe time-consuming process of lithium intercalation andde-intercalation. The super-battery is essentially intercalation-free,with most of the lithium being captured by and stored on the massivesurface areas of the cathode active material. Typically >90% of lithiumatoms are captured on graphene surfaces, and more typically less than 1%of lithium could accidentally enter the interior of a multi-layergraphene structure (since the super-battery is typically operatedbetween 1.5 and 4.5 volts). The charge/discharge time of a super-batteryis limited only by the migration of lithium ions through liquidelectrolyte (organic or ionic liquid), which is very fast and results inultra-high power densities unmatched even by the supercapacitors (whichare noted for their high power densities). This is further explained inwhat follows:

Assume that the diffusion coefficient of Li ions in a particular mediumis D and a required travel distance is x, then the required diffusiontime can be approximated as t˜x²/D, according to a well-known kineticsequation. As a first-order of approximation, the total required timescale for a lithium ion to complete a charge or discharge process may beestimated as:

t _(total)=(La/2)² /D _(electrolyte)+(d _(a)/2)² /D _(a)+(Ls)² /D_(s)+(Lc/2)² /D _(electrolyte)+(d _(c)/2)² /D _(c)  (1)

where D_(electrolyte)=Li ion diffusion coefficient in electrolyte,D_(a)=Li ion diffusion coefficient in an anode active material particle,D_(s)=Li ion diffusion coefficient through a porous separator, andD_(c)=Li ion diffusion coefficient in a cathode active materialparticle.

Representative diffusion coefficients of Li⁺ in or through variousliquid mediums or solid membrane or particles are given below (based onopen literature data): liquid electrolyte (2×10⁻⁶ cm²/s); separator(7.5×10⁻⁷ cm²/s); LiFePO₄ cathode (10⁻¹³ cm²/s); Li₃V₂(PO₄)₃ cathode(10⁻¹³ to 10⁻⁹ cm²/s); nano-Si anode (10⁻¹² cm²/s) graphite anode(1-4×10⁻¹⁰ cm²/s); and Li₄Ti₅O₁₂ anode (1.3×10⁻¹¹ cm²/s). This impliesthat, for a conventional lithium ion battery cell wherein LiFePO₄particles are used as a cathode active material, the final term,(d_(c)/2)²/D_(c), in Eq. (1) dominates the required total diffusion timedue to its excessively low diffusion coefficient. Actually, the value ofdiffusion coefficient varies between 10⁻¹⁰ and 10⁻¹⁶ cm²/s, depending onthe lithium content in solid solution Li_(X)FePO₄ and Li_(1-X)FePO₄(X<0.02) or the LiFePO₄/FePO₄ phase ratio.

In contrast, in a super-battery (partially surface-mediated cell)containing a meso-porous cathode of a non-functionalized orfunctionalized nano carbon material (e.g., graphene, CNT, or disorderedcarbon) and a lithium metal foil as the anode (schematically illustratedin FIG. 1(C)), Li ions do not have to diffuse through a solid-statecathode particle and, hence, are not subject to the limitation by a lowsolid-state diffusion coefficient at the cathode (e.g. 10⁻¹³ cm²/s in aLiFePO₄ particle). Instead, the cathode active materials are highlyporous, allowing liquid electrolyte to reach the interior of the poreswhere active surfaces are present to readily and reversibly capturelithium ions that diffuse into these pores through a liquid medium (nota solid medium) with a high diffusion coefficient (e.g., 2×10⁻⁶ cm²/s).In such a super-battery, the final term, (d_(c)/2)²/D_(c), in Eq. (1) ispractically non-existing. The required total diffusion time is nowdictated by the thicknesses of the electrodes and the separator. Theabove discussion is based on the premise that the reversible capturingstep between an active surface and a lithium ion in the electrolyte isfast, and the whole charge-discharge process is not reaction-controlled.This has been always the case.

In a prior art lithium-ion capacitor (LIC), the cathode is a meso-porousstructure of a nano carbon material (e.g., activated carbon), butlithium titanate or graphite particles constitute the anode(schematically illustrated in FIGS. 2(C) and 2(D)). In a cell dischargesituation, lithium ions must diffuse out of lithium titanate particlesor graphite particles (a slow de-intercalation step), and then migratein liquid electrolyte across the anode thickness. Subsequently, lithiumions must move (in liquid electrolyte) across a porous separator,diffuse across part of the cathode thickness in liquid electrolyte toreach a location close to a surface area of a nano-structured cathodeactive material. There is no need for solid-state diffusion at thecathode side. The whole process is essentially dictated by thesolid-state diffusion at the anode. Hence, this LIC should exhibit aslower kinetic process (hence, a lower power density) as compared to thesuper-battery (partially surface-mediated).

By plugging representative values of the various parameters in Eq. (1)we obtain the total lithium migration time required of a battery chargeor discharge process for several conventional lithium-ion battery typesand several lithium super-battery cells and LICs. The first group is aconventional lithium-ion battery with a graphite particle anode andlithium iron phosphate cathode (Gr/LiFePO₄). The second and third groupsare both conventional Li-ion batteries with a LiFePO₄ cathode and a Siparticle- or lithium titanate-based anode, respectively (Nano-Si/LiFePO₄and Li₄Ti₅O₁₂/LiFePO₄). The fourth group is a LIC (Li₄Ti₅O₁₂/f-CNM)where the anode is composed of Li₄Ti₅O₁₂ particles and the cathode isfunctionalized carbon nano material (f-CNM), such as CNT or activatedcarbon (AC). The fifth group is a partially surface-mediated cell (Lifoil/f-CNM) where the anode is a lithium foil and the cathode is acarbon nano material. These data are shown in Table 1(a) and (b) below:

TABLE 1(a) Parameters used in the present calculations (CNM = carbonnano materials, including carbon nanotubes (CNTs), nano grapheneplatelets (NGPs), disordered carbon, etc; Gr = graphite). Anode D_(li)in Cathode D_(li) in Total D_(li) in Particle anode Sep. D_(li) inparticle cathode diffusion Cell Type Electrolyte La Dia., da particlethick. separator Lc Dia., dc particle time (Anode/Cathode) cm²/s (um)(um) cm²/s (um) cm²/s (um) (um) cm²/s (sec) Gr/LiFePO₄ 1.00E−06 200 202.00E−10 100 7.50E−07 200 1  1.0E−13 3.02E+04 Gr/LiFePO₄-nano 1.00E−06200 20 2.00E−10 100 7.50E−07 200 0.1  1.0E−13 5.48E+03 Gr/LiFePO₄-nano1.00E−06 200 1 2.00E−10 100 7.50E−07 200 0.1  1.0E−13 4.96E+02Nano-Si/LiFePO₄ 1.00E−06 200 0.1 1.00E−12 100 7.50E−07 200 0.1  1.0E−135.08E+02 Li₄Ti₅O₁₂/LiFePO₄ 1.00E−06 200 0.1 1.30E−11 100 7.50E−07 2000.1  1.0E−13 4.85E+02 Li₄Ti₅O₁₂/LiFePO₄ 1.00E−06 100 0.05 1.30E−11 507.50E−07 100 0.05  1.0E−13 1.21E+02 Li₄Ti₅O₁₂/f-CNM 1.00E−06 200 0.11.30E−11 100 7.50E−07 200 0.1 1.0E−6 2.35E+02 Li₄Ti₅O₁₂/f-CNM 1.00E−0620 0.1 1.30E−11 20 7.50E−07 20 0.1 1.0E−6 5.26E+00 Li₄Ti₅O₁₂/f-CNM1.00E−06 2 0.1 1.30E−11 2 7.50E−07 2 0.1 1.0E−6 1.96E+00 Li₄Ti₅O₁₂/f-CNM1.00E−06 2 0.1 1.30E−11 2 1.00E−06 0.2 0.1 1.0E−6 1.94E+00 Li foil/f-CNM1.00E−06 10 0 1.30E−11 10 7.50E−07 0.3 0.1 1.0E−6 5.84E−01 Li foil/f-CNM1.00E−06 10 0 1.30E−11 10 7.50E−07 3 0.1 1.0E−6 6.06E−01 Li foil/f-CNM1.00E−06 30 0 1.30E−11 10 7.50E−07 30 0.1 1.0E−6 4.83E+00 Li foil/f-CNM1.00E−06 30 0 1.30E−11 10 7.50E−07 200 0.1 1.0E−6 1.03E+02

TABLE 1(b) The required diffusion time to reach a particle in the anode(t_(La)), diffusion in the anode particle (ta), diffusion time throughthe separator (ts), diffusion time to reach a cathode particle (t_(Lc)),and the diffusion time in the cathode particle (tc). Total Total t_(La)Ta Ts t_(Lc) Tc time time (sec) (sec) (sec) (sec) (sec) (sec) (hours)Cell type 1.00E+02 5.00E+03 3.33E+01 1.00E+02 1.39E+05 3.02E+04 8.40Gr/LiFePO₄ 1.00E+02 5.00E+03 3.33E+01 1.00E+02 1.39E+03 5.48E+03 1.52Gr/LiFePO₄-nano 1.00E+02 1.25E+01 3.33E+01 1.00E+02 1.39E+03 4.96E+020.138 Gr/LiFePO₄-nano 1.00E+02 2.50E+01 3.33E+01 1.00E+02 1.39E+035.08E+02 0.141 Nano-Si/LiFePO₄-n 1.00E+02 1.92E+00 3.33E+01 1.00E+021.39E+03 4.85E+02 0.135 Li₄Ti₅O₁₂/LiFePO₄-n 2.50E+01 4.81E−01 8.33E+002.50E+01 3.47E+02 1.21E+02 0.00337 Li₄Ti₅O₁₂/LiFePO₄-n 1.00E+02 1.92E+003.33E+01 1.00E+02 2.50E−05 2.35E+02 6.53E−02 Li₄Ti₅O₁₂/f-CNM 1.00E+001.92E+00 1.33E+00 1.00E+00 2.50E−05 5.26E+00 1.46E−03 Li₄Ti₅O₁₂/f-CNM1.00E−02 1.92E+00 1.33E−02 1.00E−02 2.50E−05 1.96E+00 5.43E−04Li₄Ti₅O₁₂/f-CNM 1.00E−02 1.92E+00 1.00E−02 1.00E−04 2.50E−05 1.94E+005.40E−04 Li₄Ti₅O₁₂/f-CNM 2.50E−01 0.00E+00 3.33E−01 2.25E−04 2.50E−055.84E−01 1.62E−04 Li foil/f-CNM 2.50E−01 0.00E+00 3.33E−01 2.25E−022.50E−05 6.06E−01 1.68E−04 Li foil/f-CNM 2.25E+00 0.00E+00 3.33E−012.25E+00 2.50E−05 4.83E+00 1.34E−03 Li foil/f-CNM 2.25E+00 0.00E+003.33E−01 1.00E+02 2.50E−05 1.03E+02 2.85E−02 Li foil/f-CNM

Several significant observations can be made from the data of Table 1(a)and (b):

-   -   (1) Conventional lithium ion batteries (first group above)        featuring a micron-sized graphite particle anode (graphite        diameter=20 μm) and a micron-sized LiFePO₄ cathode (particle        diameter=1 μm) would require several hours (e.g. 8.4 h) to        complete the required lithium ion diffusion process. This is why        conventional lithium ion batteries exhibit very low power        densities (typically 100-500 W/Kg) and very long re-charge        times.    -   (2) For a prior art lithium-ion capacitor (LIC) featuring a        carbon cathode (e.g. activated carbon or f-CNT) and an anode of        Li₄Ti₅O₁₂ nano particles, the required diffusion times are        between 235 sec (<4 minutes) for a cathode thickness of 200 μm        and 1.96 sec for an ultra-thin cathode (e.g., 0.3 μm LBL f-CNT        as prepared by the layer-by-layer method of the MIT research        group [S. W. Lee, et al, Nature Nanotechnology, 5 (2010)        531-537]). Unfortunately, such an ultra-thin electrode (0.3-3        μm) is of extremely limited utility value.    -   (3) For the lithium super-batteries (partially        surface-mediated), the electrode thickness is a dominating        factor. For instance, in the case of using lithium metal foil as        the anode (Type-1 super-battery), the total diffusion time can        be as short as <0.6 sec (when the cathode thickness is 0.3 μm or        3 μm), which increases to 103 sec (still less than 2 minutes)        when the cathode thickness is 200 μm.    -   (4) The above observations imply that the lithium        super-batteries should have an extraordinary power density,        particularly when the electrodes are ultra-thin. This is why        Lee, et al. at MIT were able to report a power density of 100        Kw/Kg for their lithium super-battery cells having a LBL f-CNT        cathode of 0.3 μm thick and a lithium foil anode. However, a        useful electrode size is at least 50 μm in thickness (typically        between 100 and 300 μm) and, again, the cells with a cathode        thickness of 0.3-3.0 μm have very limited practical utility        value. The exceptionally high power densities observed for the        lithium super-batteries with a LBL f-CNT cathode reported by        Lee, et al are due to the ultra-thin cathode thickness (0.3 μm).        As shown in FIG. 8, our graphene-based partially        surface-mediated cells (typically having an electrode thickness        of 100-300 μm) perform even better than the thin electrode-based        LBL f-CNT cell (also partially surface mediated).

It may be noted that, for the lithium super-battery discussed above, theanode has a current collector and a lithium foil as a lithium ionsource, and there is no other anode active material in a particulateform and, hence, no particle diameter (d_(a) was assigned as zero in theabove calculation). During the first discharge, Li foil iselectrochemically ionized to release ions.

An alternative form of the partially surface-mediated cell (Type-2super-battery) contains a lithiated compound or lithium-intercalationcompound implemented at the anode as a lithium source, not as an anodeactive material (or implemented at the cathode, but not serving as acathode active material). During the first discharge of such asuper-battery (e.g. having graphite particles pre-intercalated withlithium), a majority of the lithium stored in this lithiated compoundcan be extracted out using a properly selected first discharge voltagerange. This amount of lithium is then fully captured by the massivegraphene surfaces at the cathode. During the subsequent re-charge (andthe many discharge/charge cycles that follow), the operating voltagerange of such a super-battery is limited to the range from 1.5 volts to4.5 volts. The utilization of this second voltage range as the actualcell operating range for an end-user (e.g. a consumer of a super-batteryused in a mobile phone) would prevent the returning lithium ions at theanode (during re-charge) from undergoing intercalation into the bulk ofa graphite particle. The returning lithium ions are simplyelectro-chemically plated onto the anode current collector and thesurfaces of these graphite particles. Since lithium ionization andsurface deposition are fast processes, this second type of super-batteryexhibits a high power density. Furthermore, due to the full utilizationof the originally pre-loaded lithium, the amount of lithium ions thatcan be exchanged between the anode surfaces and cathode active materialsurfaces (e.g. non-functionalized graphene) can be huge.

By contrast, the operation of prior art lithium-ion capacitors (e.g.those LICs having a prelithiated graphite anode and activated carboncathode) is limited to 2.2 volts and 3.8 volts and the amount of lithiumions that can be exchanged between the anode and the cathode has beenvery low, typically lower than that of a super-battery by a factor of5-10. Such a huge difference in performance between a conventional LICand a Type-2 super-battery of the present invention is due to materialcomposition differences in the electrode(s), and the differences inoperating methods. This super-battery strategy (using a graphenecathode, and a different operating voltage range) has been most noveland innovative, and the results have been most surprising.

Partially Surface-Controlled Battery Device Versus Prior ArtSupercapacitors

This new partially surface-mediated, lithium ion-exchanging batterydevice is also patently distinct from the conventional supercapacitor inthe following aspects:

-   -   (1) The conventional or prior art supercapacitors do not have a        lithium ion source implemented at the anode when the cell is        made.    -   (2) The electrolytes used in these prior art supercapacitors are        mostly lithium-free or non-lithium-based. Even when a lithium        salt is used in a supercapacitor electrolyte, the solubility of        lithium salt in a solvent essentially sets an upper limit on the        amount of lithium ions that can participate in the formation of        electric double layers of charges inside the electrolyte phase        (near but not on an electrode material surface, as illustrated        in FIGS. 2(A) and 2(B)). As a consequence, the specific        capacitance and energy density of the resulting supercapacitor        are relatively low (e.g. typically <6 Wh/kg based on total cell        weight), as opposed to, for instance, 160 Wh/kg (based on total        cell weight) of the presently invented surface-mediated cells.    -   (3) The prior art supercapacitors are based on either the        electric double layer (EDL) mechanism or the pseudo-capacitance        mechanism to store their charges. In both mechanisms, no massive        lithium ions are exchanged between the two electrodes (even when        a lithium salt is used in electrolyte). There are equal amounts        of cations and anions that participate in the charge storage.        When an EDL supercapacitor is charged, for instance, the        activated carbon particle surfaces at the anode are negatively        charged which attract the cations (e.g. Li⁺ if lithium salt is        used in the electrolyte) to the anode side and these cations        form electric double layers of charges near the surfaces of an        electrode active material (but not on the surface). The cations        are not captured or stored in or on the surfaces of the        electrode active material. Similarly, the negatively charged        activated carbon particles at the cathode attract the anions        (e.g. PF₆ ⁻) to the cathode side, also forming an electric        double layer near the cathode material surface.        -   In contrast, when a super-battery of the present invention            is charged, essentially all of the lithium ions are            electro-plated back to the surface of the anode current            collector or a surface of the remaining lithium source, as            illustrated in FIG. 3(C). This is a surface deposition            process and the surface can accommodate a thick layer of            lithium atoms (not ions).    -   (4) When a supercapacitor is discharged, the cations move away        from the anode material surface and the anions move away from        the cathode material surface, but both cations and anions are        simply randomly distributed in the electrolyte (normally with        one cation staying nearby an anion). The cations (e.g. Li⁺) do        not move all the way back to the cathode side. They are        practically everywhere in the electrolyte phase.        -   In contrast, using graphene as an example of a cathode            active material in a partially surface-mediated cell of the            present invention, massive lithium ions are ionized from the            lithium source or anode current collector surface, migrate            all the way through the liquid electrolyte to the cathode            side, and get captured by or trapped at the defect sites,            graphene edges, or benzene ring centers of a graphene plane.            In our co-pending application (U.S. patent application Ser.            No. 12/928,927), functional groups on graphene surfaces are            used to capture lithium. In the instant application, a            non-functionalized material (having no functional group)            with high surface areas in direct contact with liquid            electrolyte use the benzene ring centers and surface defects            of graphene sheets to capture lithium ions from electrolyte            (FIGS. 4(D) and 4(E)). These active sites of graphene have            essentially removed lithium ions out of the liquid phase.    -   (5) The prior art symmetric supercapacitors (EDL        supercapacitors) using a lithium salt-based organic electrolyte        operate only in the range of 0-3 volts (more typically 0-2.5        volts). They cannot operate above 3 volts; there is no        additional charge storing capability beyond 3 volts and actually        the organic electrolyte typically begins to break down at 2.7        volts. In contrast, the partially surface-mediated cells of the        present invention operate typically in the range of 1.0-4.5        volts, most typically in the range of 1.5-4.5 volts), but        preferably in the range of 1.5-4.0 volts. These two ranges of        operating voltage are reflections of totally distinct charge        storage mechanisms. Even though, on the paper, there appears to        be an overlap of 1.5-3.0 volts between these two voltage ranges        (range of 1-3 and range of 1.5-4.5 volts), this overlap is        artificial, sheer coincidental, and not scientifically        meaningful since the charge storage mechanisms are fundamentally        different.    -   (6) The prior art EDL supercapacitors typically have an        open-circuit voltage of 0 or nearly zero volt. In contrast, the        super-battery typically has an open-circuit voltage of >0.6        volts, more commonly >1.0 volts, and most commonly >1.5 volts.        Most significantly, when a supercapacitor is in a discharged        state or when the cell is made (e.g., as illustrated in FIG.        5(A)), the anode and the cathode are at identical        electrochemical potential, both being significantly higher than        2.0 volts with respect to Li/Li⁺. As an organic        electrolyte-based supercapacitor cell is charged, the cathode        becomes increasingly more positive and the anode becomes more        negative, and the resulting cell voltage (which is the        difference between these two electrochemical potential values)        becomes greater and greater, reaching an upper limit of        typically 2.5-2.7 volts.        -   When the supercapacitor is discharged, the cathode potential            decreases and anode increases. As a result, the cell voltage            continues to decrease until it drops to essentially 0 volt.            In contrast, the anode chemical potential in a super-battery            remains essentially constant (near 0 volt) throughout the            charge or discharge process. But the cathode electrochemical            potential varies between approximately 1.5 volts and 4.5            volts, as illustrated in FIG. 5(B). Hence, the super-battery            cell also operates in a voltage range of approximately 1.5            volts and 4.5 volts.

Charge Storage Mechanisms and Energy Density Considerations

Not wishing to be limited by theory, but we think that the specificcapacity of an electrode in a partially surface-mediated, Li-ionexchanging cell is governed by the number of active sites on graphenesurfaces of a nano-structured carbon material at the cathode that arecapable of capturing lithium ions therein or thereon. Thenano-structured carbon material may be selected from activated carbon(AC), carbon black (CB), hard carbon, soft carbon, exfoliated graphite(EG), and isolated graphene sheets (nano graphene platelet or NGP) fromnatural graphite or artificial graphite. These carbon materials have acommon building block—graphene or graphene-like aromatic ring structure.We think that there are four possible lithium storage mechanisms:

-   -   Mechanism 1: The geometric center of a benzene ring in a        graphene plane is an active site for a lithium atom to adsorb        onto;    -   Mechanism 2: The defect site on a graphene sheet is capable of        trapping a lithium ion;    -   Mechanism 3: The cations (Li⁺) and anions (from a Li salt, such        as PF₆ ⁻) in the liquid electrolyte are capable of forming        electric double layers of charges near the electrode material        surfaces;    -   Mechanism 4: A functional group on a graphene surface/edge can        form a redox pair with a lithium ion. This mechanism does not        operate in the presently invented super-capacitor cell since        there is no functional group at the cathode.

Surface Bonding Mechanism (Mechanism 1):

Lithium atoms are capable of forming stable interactions with C atoms ona graphene plane when electrolyte is not present to compete for lithium.The Li—C bond in such a layer (without a functional group) would notresult in an sp² to an sp³ transition of carbon orbitals. Energycalculations have indicated the possible stability of such Liatom-adsorbed graphene layers (with lithium atoms bonded to the centersof benzene rings of a graphene plane) without the presence ofelectrolyte. We have surprisingly observed that the Li-bonded graphenelayer (FIG. 4(D)) can be spontaneously formed in the presence ofelectrolyte. This was unexpected since lithium ions have excellentchemical compatibility with other ingredients in the electrolyte (thisis why they naturally exist in the electrolyte) and these ingredients(e.g. solvent) would compete against the graphene surface for trying tokeep the lithium ions in the solvent phase, as opposed to being“high-jacked” by graphene surface. The bonding between lithium atoms andgraphene surface has been most surprisingly strong.

Lithium Ion Trapping at Defect Sites (Mechanism 2):

Active defects such as edges and vacancies (e.g. FIG. 4(E)) incarbonaceous materials might be capable of accommodating additional Li.There are a large number of these defects or disorder sites in NGPsinevitably induced by the oxidation and reduction processes commonlyused for graphene production.

Electric Double Layer (EDL) (Mechanism 3):

The super-battery electrolyte is typically composed of a lithium ionsalt dissolved in a solvent. The electrolytic salts can be selected fromlithium perchlorate (LiClO₄), lithium hexafluorophosphate (LiPF₆),lithium borofluoride (LiBF₄), lithium hexafluoroarsenide (LiAsF₆), andlithium trifluoro-metasulfonate (LiCF₃SO₃), etc. In principle, asillustrated in FIG. 4(C), some electric double layers (EDL) may beconceptually formed by cations (e.g. Li⁺) and their counter ions (e.g.PF₆ ⁻ and BF₄ ⁻ anions) and this EDL contribution to the energy storagecapacity of a SMC cell is governed by the electrolytic saltconcentration in solvent.

Given a sufficient amount of electrode surface areas, the maximumcontribution of Mechanism 3 to the overall charge storage capacity isdictated by the concentration of cations or anions. The EDL mechanismtypically contributes to less than approximately 10% (more typically<5%) of the total lithium ion storage capacity of a super-battery.

Formation of Redox Pairs (Mechanism 4):

A surface redox reaction can occur between a lithium ion and afunctional group (if any), such as carbonyl (>C═O) or carboxylic group(—COOH), as illustrated in FIG. 4(A). The presence of functional groups,such as —COOH and >C═O, in chemically prepared graphene oxide have beenwell documented. The formation of these functional groups is a naturalresult of the oxidizing reactions of graphite by sulfuric acid andstrong oxidizing agents (e.g. nitric acid and potassium permanganatecommonly used in the preparation of graphene oxide). Both un-separatedgraphite worms (exfoliated graphite) and the separated graphene sheets(NGPs) can have surface- or edge-borne functional groups. This is theprimary lithium storing mechanism disclosed in our co-pendingapplication (U.S. patent application Ser. No. 12/928,927). Thesuper-battery in the instant application is based mainly upon Mechanisms1 and 2.

In general, the electric double layer mechanism contributes to less than10% (mostly less than 5%) of the charge storage capacity of asuper-battery. When the cathode contains some multi-layer grapheneplatelets, there might be some intercalation of lithium into the bulk ofan active material if the super-battery operating voltage goes below 1.5volts. Even in this case, no more than 20% (typically <<10%) of thelithium is stored in the bulk of the cathode active material when thedevice is in a discharged state.

Nano-structured materials for use in the cathode of the instantinvention may preferably contain nano graphene platelet (NGP), carbonnano-tube (CNT), or disordered carbon. The CNT is a better knownmaterial in the nano material industry and, hence, will not be furtherdiscussed herein. What follows is a description of NGP andnano-structured disordered carbon:

Nano Graphene Platelet (NGP)

The applicant's research group was the first in the world to discoversingle-layer graphene [B. Z. Jang and W. C. Huang, “Nano-scaled GraphenePlates,” U.S. patent application Ser. No. 10/274,473 (Oct. 21, 2002);now U.S. Pat. No. 7,071,258 (Jul. 4, 2006)] and the first to usegraphene for supercapacitor [L. Song, A. Zhamu, J. Guo, and B. Z. Jang“Nano-scaled Graphene Plate Nanocomposites for SupercapacitorElectrodes” U.S. patent application Ser. No. 11/499,861 (Aug. 7, 2006),now U.S. Pat. No. 7,623,340 (Nov. 24, 2009)], and for lithium-ionbattery applications [A. Zhamu and B. Z. Jang, “Nano GraphenePlatelet-Based Composite Anode Compositions for Lithium Ion Batteries,”U.S. patent application Ser. No. 11/982,672 (Nov. 5, 2007), now U.S.Pat. No. 7,745,047 (Jun. 29, 2010)].

Single-layer graphene or the graphene plane (a layer of carbon atomsforming a hexagonal or honeycomb-like structure) is a common buildingblock of a wide array of graphitic materials, including naturalgraphite, artificial graphite, soft carbon, hard carbon, coke, activatedcarbon, carbon black, etc. In these graphitic materials, typicallymultiple graphene sheets are stacked along the graphene thicknessdirection to form an ordered domain or crystallite of graphene planes.Multiple crystallites of domains are then connected with disordered oramorphous carbon species. In the instant application, we are able toextract or isolate these crystallites or domains to obtainmultiple-layer graphene platelets out of the disordered carbon species.In some cases, we exfoliate and separate these multiple-grapheneplatelets into isolated single-layer graphene sheets. In other cases(e.g. in activated carbon, hard carbon, and soft carbon), we chemicallyremoved some of the disordered carbon species to open up gates, allowingliquid electrolyte to enter into the interior (exposing graphenesurfaces to electrolyte).

In the present application, nano graphene platelets (NGPs) or “graphenematerials” collectively refer to single-layer and multi-layer versionsof graphene, graphene oxide (slightly oxidized graphene having nofunctional group for lithium reaction), graphene fluoride, hydrogenatedgraphene, nitrogenated graphene, doped graphene, etc.

For the purpose of defining the geometry of an NGP, the NGP is describedas having a length (the largest dimension), a width (the second largestdimension), and a thickness. The thickness is the smallest dimension,which is no greater than 100 nm and, in the present application, nogreater than 10 nm (preferably no greater than 5 nm). The NGP may besingle-layer graphene. When the platelet is approximately circular inshape, the length and width are referred to as diameter. In thepresently defined NGPs, there is no limitation on the length and width,but they are preferably smaller than 10 μm and more preferably smallerthan 1 μm. We have been able to produce NGPs with length smaller than100 nm or larger than 10 μm. The NGP can be pristine graphene (withessentially 0% oxygen content, typically <2% oxygen) or graphene oxide(typically from 5% up to approximately 45% by weight oxygen). Grapheneoxide can be thermally or chemically reduced to become reduced grapheneoxide (typically with an oxygen content of 1-20%, mostly below 5% byweight). For use in the cathode of the functional material-basedsuper-battery disclosed in our earlier application, the oxygen contentwas preferably in the range of 5% to 30% by weight, and more preferablyin the range of 10% to 30% by weight. However, in the instantapplication, the super-battery electrode typically has less than 5%oxygen (hence, essentially functional group-free) and, in many cases,less than 2%. The graphene specific surface area accessible to liquidelectrolyte is the single most important parameter in dictating theenergy and power densities of a super-battery.

Despite the fact that individual graphene sheets have an exceptionallyhigh specific surface area, flat-shaped graphene sheets prepared byconventional routes have a great tendency to re-stack together oroverlap with one another, thereby dramatically reducing the specificsurface area that is accessible by the electrolyte. FIG. 6(A) shows anew breed of graphene that is herein referred to as the curved grapheneplatelet or sheet. Curved NGPs are capable of forming a meso-porousstructure having a desired pore size range (e.g. slightly >2 nm) whenthey were stacked together to form an electrode. This size range appearsto be conducive to being accessible by the commonly usedlithium-containing electrolytes.

The curved NGPs may be produced by using the following recommendedprocedures:

-   (a) dispersing or immersing a laminar graphite material (e.g.,    natural graphite powder) in a mixture of an intercalant and an    oxidant (e.g., concentrated sulfuric acid and nitric acid,    respectively) to obtain a graphite intercalation compound (GIC) or    graphite oxide (GO);-   (b) exposing the resulting GIC or GO to a thermal shock, preferably    in a temperature range of 600-1,100° C. for a short period of time    (typically 15 to 60 seconds), to obtain exfoliated graphite or    graphite worms (some oxidized NGPs with a thickness <100 nm could be    formed at this stage if the intercalation/oxidation step was allowed    to proceed for a sufficiently long duration of time; e.g. >24    hours);-   (c) dispersing the exfoliated graphite to a liquid medium to obtain    a graphene-liquid suspension (a functionalizing agent may be added    into this suspension if functional groups are desired, as in our    co-pending application);-   (d) aerosolizing the graphene-liquid suspension into liquid droplets    while concurrently removing the liquid to recover curved NGPs.    Without the aerosolizing step, the resulting graphene platelets tend    to be flat-shaped.

It may be noted that steps (a) to (b) are the most commonly used stepsto obtain exfoliated graphite (FIG. 6B) and graphene oxide platelets inthe field. Step (d) is essential to the production of curved graphenesheets. Oxidized NGPs or GO platelets may be chemically reduced torecover conductivity properties using hydrazine as a reducing agent,before, during, or after chemical functionalization.

In 2007, we reported a direct ultrasonication method of producingpristine nano graphene directly from graphite particles dispersed in asurfactant-water suspension [A. Zhamu, et al, “Method of ProducingExfoliated Graphite, Flexible Graphite, and Nano-Scaled GraphenePlates,” U.S. patent application Ser. No. 11/800,728 (May 8, 2007)].This method entails dispersing natural graphite particles in a lowsurface tension liquid, such as acetone or hexane. The resultingsuspension is then subjected to direct ultrasonication for 10-120minutes, which produces graphene at a rate equivalent to 20,000 attemptsto peel off graphene sheets per second per particle. The graphite hasnever been intercalated or oxidized and, hence, requires no subsequentchemical reduction. This method is fast, environmentally benign, and canbe readily scaled up, paving the way to the mass production of pristinenano graphene materials. The same method was later studied by others andnow more commonly referred to as the “liquid phase production.”

Nano-Structured Disordered Carbon

The disordered carbon material may be selected from a broad array ofcarbonaceous materials, such as a soft carbon, hard carbon, polymericcarbon (or carbonized resin), meso-phase carbon, coke, carbonized pitch,carbon black, activated carbon, or partially graphitized carbon. Adisordered carbon material is typically formed of two phases wherein afirst phase is small graphite crystal(s) or small stack(s) of graphiteplanes (with typically up to 10 graphite planes or aromatic ringstructures overlapped together to form a small ordered domain) and asecond phase is non-crystalline carbon, and wherein the first phase isdispersed in the second phase or bonded by the second phase. The secondphase is made up of mostly smaller molecules, smaller aromatic rings,defects, and amorphous carbon. Typically, the disordered carbon ishighly porous (e.g., activated carbon) or present in an ultra-finepowder form (e.g. carbon black) having nano-scaled features (hence, ahigh specific surface area).

Soft carbon refers to a carbonaceous material composed of small graphitecrystals wherein the orientations of these graphite crystals or stacksof graphene sheets are conducive to further merging of neighboringgraphene sheets or further growth of these graphite crystals or graphenestacks using a high-temperature heat treatment (graphitization). Hence,soft carbon is said to be graphitizable.

Hard carbon refers to a carbonaceous material composed of small graphitecrystals wherein these graphite crystals or stacks of graphene sheetsare not oriented in a favorable directions (e.g. nearly perpendicular toeach other) and, hence, are not conducive to further merging ofneighboring graphene sheets or further growth of these graphite crystalsor graphene stacks (i.e., not graphitizable).

Carbon black (CB), acetylene black (AB), and activated carbon (AC) aretypically composed of domains of aromatic rings or small graphenesheets, wherein aromatic rings or graphene sheets in adjoining domainsare somehow connected through some chemical bonds in the disorderedphase (matrix). These carbon materials are commonly obtained fromthermal decomposition (heat treatment, pyrolyzation, or burning) ofhydrocarbon gases or liquids, or natural products (wood, coconut shells,etc).

The preparation of polymeric carbons by simple pyrolysis of polymers orpetroleum/coal tar pitch materials has been known for approximatelythree decades. When polymers such as polyacrylonitrile (PAN), rayon,cellulose and phenol formaldehyde were heated above 300° C. in an inertatmosphere they gradually lost most of their non-carbon contents. Theresulting structure is generally referred to as a polymeric carbon.Depending upon the heat treatment temperature (HTT) and time, polymericcarbons can be made to be insulating, semi-conducting, or conductingwith the electric conductivity range covering approximately 12 orders ofmagnitude. This wide scope of conductivity values can be furtherextended by doping the polymeric carbon with electron donors oracceptors. These characteristics uniquely qualify polymeric carbons as anovel, easy-to-process class of electro-active materials whosestructures and physical properties can be readily tailor-made.

Polymeric carbons can assume an essentially amorphous structure, or havemultiple graphite crystals or stacks of graphene planes dispersed in anamorphous carbon matrix. Depending upon the HTT used, variousproportions and sizes of graphite crystals and defects are dispersed inan amorphous matrix. Various amounts of two-dimensional condensedaromatic rings or hexagons (precursors to graphene planes) can be foundinside the microstructure of a heat treated polymer such as a PAN fiber.An appreciable amount of small-sized graphene sheets are believed toexist in PAN-based polymeric carbons treated at 300-1,000° C. Thesespecies condense into wider aromatic ring structures (larger-sizedgraphene sheets) and thicker plates (more graphene sheets stackedtogether) with a higher HTT or longer heat treatment time (e.g., >1,500°C.). These graphene platelets or stacks of graphene sheets (basalplanes) are dispersed in a non-crystalline carbon matrix. Such atwo-phase structure is a characteristic of some disordered carbonmaterial.

There are several classes of precursor materials to the disorderedcarbon materials of the instant patent application. For instance, thefirst class includes semi-crystalline PAN in a fiber form. As comparedto phenolic resin, the pyrolized PAN fiber has a higher tendency todevelop small crystallites that are dispersed in a disordered matrix.The second class, represented by phenol formaldehyde, is a moreisotropic, essentially amorphous and highly cross-linked polymer. Thethird class includes petroleum and coal tar pitch materials in bulk orfiber forms. The precursor material composition, heat treatmenttemperature (HTT), and heat treatment time (Htt) are three parametersthat govern the length, width, thickness (number of graphene planes in agraphite crystal), and chemical composition of the resulting disorderedcarbon materials.

In the present investigation, PAN fibers were subjected to oxidation at200-350° C. while under a tension, and then partial or completecarbonization at 350-1,500° C. to obtain polymeric carbons with variousnano-crystalline graphite structures (graphite crystallites). Selectedsamples of these polymeric carbons were further heat-treated at atemperature in the range of 1,500-2,000° C. to partially graphitize thematerials, but still retaining a desired amount of amorphous carbon (noless than 10%). Phenol formaldehyde resin and petroleum and coal tarpitch materials were subjected to similar heat treatments in atemperature range of 500 to 1,500° C. The disordered carbon materialsobtained from PAN fibers or phenolic resins are preferably subjected toactivation using a process commonly used to produce activated carbon(e.g., treated in a KOH melt at 900° C. for 1-5 hours). This activationtreatment is intended for making the disordered carbon meso-porous,enabling liquid electrolyte to reach the edges or surfaces of theconstituent aromatic rings after the super-battery device is made. Suchan arrangement enables the lithium ions in the liquid to readily depositonto graphene surfaces without having to undergo solid-state diffusion.

Certain grades of petroleum pitch or coal tar pitch may be heat-treated(typically at 250-500° C.) to obtain a liquid crystal-type, opticallyanisotropic structure commonly referred to as meso-phase. Thismeso-phase material can be extracted out of the liquid component of themixture to produce meso-phase particles or spheres.

Physical or chemical activation may be conducted on all kinds ofdisordered carbon (e.g. a soft carbon, hard carbon, polymeric carbon orcarbonized resin, meso-phase carbon, coke, carbonized pitch, carbonblack, activated carbon, or partially graphitized carbon) to obtainactivated disordered carbon. For instance, the activation treatment canbe accomplished through oxidizing, CO₂ physical activation, KOH or NaOHchemical activation, or exposure to nitric acid, fluorine, or ammoniaplasma (for the purpose of creating electrolyte-accessible pores, notfor functionalization).

In summary, the cathode active material of the presently inventednon-functionalized material-based super-battery may be selected from (a)A porous disordered carbon material selected from a soft carbon, hardcarbon, polymeric carbon or carbonized resin, meso-phase carbon, coke,carbonized pitch, carbon black, activated carbon, or partiallygraphitized carbon; (b) A graphene material selected from a single-layersheet or multi-layer platelet of graphene, lightly oxidized grapheneoxide, graphene fluoride, hydrogenated graphene, nitrogenated graphene,boron-doped graphene, nitrogen-doped graphene, non-functionalizedgraphene, or reduced graphene oxide; (c) Exfoliated graphite; (d)Meso-porous carbon; (e) A carbon nanotube selected from a single-walledcarbon nanotube or multi-walled carbon nanotube; (f) A carbonnano-fiber, metal nano-wire, metal oxide nano-wire or fiber, orconductive polymer nano-fiber, or (g) A combination thereof.

The present invention also provides a method of operating a lithiumsuper-battery cell, said method including: (A) Providing a lithiumsuper-battery cell comprising an anode, a lithium source, a porousseparator, liquid or gel electrolyte, and a cathode, wherein the cathodehas a non-functionalized material having lithium-capturing surfaces andsaid cell has an open-circuit voltage from 0.5 volts to 2.0 volts; (B)Releasing lithium ions from the lithium source into the electrolyteduring the first discharge of the cell; and (C) Exchanging lithium ionsbetween the anode and the lithium-capturing surfaces of the cathodeduring a subsequent charge or discharge in a cell operating in a voltagerange of 1.5 volts and 4.5 volts.

Preferably and typically, both the charge and discharge of the cell donot involve lithium intercalation or solid state diffusion. Preferably,the lithium source is a prelithiated compound or lithium intercalationcompound (in a Type-2 lithium super-battery) and step (B) of releasinglithium ions from the lithium source occurs in a first voltage range,and wherein an operation of the cell occurs in a second voltage rangedifferent from the first voltage range. Preferably, the lithium sourceis a prelithiated graphite, prelithiated carbon material, lithiatedtitanium dioxide, lithium titanate, lithium manganate, a lithiumtransition metal oxide, Li₄Ti₅O₁₂, or a combination thereof

The present invention provides yet another method of operating a lithiumsuper-battery cell, the method including: (A) Providing a lithiumsuper-battery cell comprising an anode, a lithium source, a porousseparator, electrolyte having an initial amount of lithium ions, and acathode, wherein the cathode has a material having lithium-capturingsurfaces in contact with said electrolyte; (B) Releasing lithium ionsfrom the lithium source into the electrolyte during the first dischargeof the cell; (C) Operating the cathode to capture lithium ions from theelectrolyte and store the captured lithium on cathode surfaces; and (D)Exchanging an amount of lithium ions, greater than the initial amount,between the anode and the lithium-capturing surfaces of the cathodeduring a subsequent charge or discharge operation.

The following examples serve to illustrate the preferred embodiments ofthe present invention and should not be construed as limiting the scopeof the invention:

Example 1 Functionalized and Non-Functionalized Soft Carbon (One Type ofDisordered Carbon), and Soft Carbon-Based Super-Battery Cells

Non-functionalized and functionalized soft carbon materials wereprepared from a liquid crystalline aromatic resin. The resin was groundwith a mortar, and calcined at 900° C. for 2 h in a N₂ atmosphere toprepare the graphitizable carbon or soft carbon. The resulting softcarbon was mixed with small tablets of KOH (four-fold weight) in analumina melting pot. Subsequently, the soft carbon containing KOH washeated at 750° C. for 2 h in N₂. Upon cooling, the alkali-rich residualcarbon was washed with hot water until the outlet water reached a pHvalue of 7. The resulting material is activated, but non-functionalizedsoft carbon.

Separately, some portion of the activated soft carbon was then immersedin a 90% H₂O₂-10% H₂O solution at 45° C. for an oxidation treatment thatlasted for 2 hours. Then, the resulting partially oxidized soft carbonwas immersed in HCOOH at room temperature for functionalization for 24hours. The resulting functionalized soft carbon was dried by heating at60° C. in a vacuum oven for 24 hours.

Coin cells using functionalized soft carbon as a cathode, a sheet ofcurrent collector, a thin piece of lithium foil as a lithium sourceimplemented between an anode current collector and a separator layer(Sample-1A) were made and tested. Corresponding cells withoutfunctionalization (Sample-1B) were also prepared and tested forcomparison. In all cells, the separator used was one sheet ofmicro-porous membrane (Celgard 2500). The current collector for each ofthe two electrodes was a piece of carbon-coated aluminum foil. Theelectrode was a composite composed of 85 wt. % soft carbon (+5% Super-Pand 10% PTFE binder coated on Al foil). The electrolyte solution was 1 MLiPF₆ dissolved in a mixture of ethylene carbonate (EC) and dimethylcarbonate (DMC) with a 3:7 volume ratio. The separator was wetted by aminimum amount of electrolyte to reduce the background current. Cyclicvoltammetry and galvanostatic measurements of the lithium cells wereconducted using an Arbin 32-channel supercapacitor-battery tester atroom temperature (in some cases, at a temperature as low as −40° C. andas high as 60° C.).

Galvanostatic studies of the super-battery (Sample-1A) with afunctionalized soft carbon-based bulk material (thickness >200 μm) as acathode active material and those of the correspondingnon-functionalized material-based super-battery cell (Sample-1B) haveenabled us to obtain significant data as summarized in the Ragone plotof FIG. 7(A) and cycling stability data (FIG. 7(B)). These plots allowus to make the following observations:

-   -   (a) Both super-battery cells (with a functionalized or        non-functionalized cathode material) exhibit significantly        higher energy densities and power densities than those of the        corresponding symmetric supercapacitors and those of the prior        art supercapacitor composed of a functionalized LBL CNT anode        and a functionalized LBL-CNT cathode of Lee, et al (both        supercapacitors having no lithium foil as a lithium source).        Actually, the two symmetric supercapacitors (without a lithium        source), based on either disordered carbon or functionalized LBL        CNT, exhibit almost identical Ragone plots even though the two        electrodes are dramatically different in thickness (>100 μm for        the disordered carbon electrode and <3.0 μm for the LBN-CNT        electrode). This is likely a manifestation of the local electric        double layer mechanism associated with a conventional        supercapacitor that does not require long-range transport of the        charges (in particular, requiring no exchange of lithium ions        between the anode and the cathode). The amounts of lithium ions        and their counter-ions (anions) are limited by the solubility of        a lithium salt in the solvent. The amounts of lithium that can        be captured and stored in the active material surfaces of the        cathode in super-batteries are dramatically higher than this        solubility limit.    -   (b) As mentioned earlier in the Background section, the power        density of a state-of-the-art supercapacitor is typically of        5,000-10,000 W/Kg, but that of a lithium-ion battery is 100-500        W/kg. This implies that the presently invented partially        surface-mediated lithium ion-exchanging cells have an energy        density comparable to that of a modern battery, which is 5-16        times higher than the energy density of conventional        supercapacitors. The super-battery cells also exhibit a power        density (or charge-discharge rates) significantly higher than        the power density of conventional electrochemical        supercapacitors.    -   (c) Most significantly, the non-functionalized material-based        partially surface-mediated cells exhibit much better cycle        stability as compared to the corresponding functional        material-based cells. As demonstrated in FIG. 7(B), the        non-functionalized surface cell maintains a high energy density        even after 2500 charge/discharge cycles. However, the        functionalized surface-controlled cell suffers a faster decay        with repeated charges/discharges. We believe that the functional        groups have a propensity to chemically react with some chemical        species in the electrolyte, resulting in a gradual reduction in        useful functional groups for forming a redox pair with lithium.        This was evidenced by the liquid electrolyte turning in color        from dark blue to yellowish after 1000 cycles in the cell        containing a functionalized material cathode.

The cells of Sample-1A work on the redox reactions of lithium ions withselect functional groups on the surfaces/edges of aromatic rings at thecathode side. These functional groups, attached to both the edge andplane surfaces of aromatic rings (small graphene sheets), are capable ofrapidly and reversibly react with lithium. The super-battery cells(Sample-1B) based on non-functionalized surfaces perform even better.The partially surface-mediated lithium ion-exchanging battery of thepresent invention is a revolutionary new energy storage device thatfundamentally differs from a supercapacitor and a lithium-ion battery.In terms of both energy density and power density, neither conventionallithium-ion battery or supercapacitor even comes close.

Example 2 NGPs from Sulfuric Acid Intercalation and Exfoliation of MCMBs

MCMB 2528 microbeads (Osaka Gas Chemical Company, Japan) have a densityof about 2.24 g/cm³; a median size of about 22.5 microns, and aninter-planar distance of about 0.336 nm. MCMB 2528 (10 grams) wereintercalated with an acid solution (sulfuric acid, nitric acid, andpotassium permanganate at a ratio of 4:1:0.05) for 24 hours. Uponcompletion of the reaction, the mixture was poured into deionized waterand filtered. The intercalated MCMBs were repeatedly washed in a 5%solution of HCl to remove most of the sulphate ions. The sample was thenwashed repeatedly with deionized water until the pH of the filtrate wasneutral. The slurry was dried and stored in a vacuum oven at 60° C. for24 hours. The dried powder sample was placed in a quartz tube andinserted into a horizontal tube furnace pre-set at a desiredtemperature, 600° C. for 30 seconds to obtain exfoliated graphite. Theexfoliated MCMB sample was subjected to further functionalization informic acid at 25° C. for 30 minutes in an ultrasonication bath toobtain functionalized graphene (f-NGP). Non-functionalized NGPs werealso obtained via ultrasonication of exfoliated MCMBs in water withoutany functionalizing agent.

For a functionalized or non-functionalized super-battery, NGPs were usedas a cathode active material. A lithium foil was added between the anodeand the separator. The Ragone plot for these two types of cells is shownin FIG. 8(A). Both of the NGP-based, partially surface-mediated, lithiumion-exchanging battery devices exhibit excellent energy densities andpower densities. The non-functionalized material-based device performsslightly better than the functionalized counterpart in terms of energydensity and power density. Also quite significantly and surprisingly, ascompared with the functionalized one, the non-functionalizedmaterial-based super-battery exhibits a much better long-term stabilityas repeated charges/discharges continue (FIG. 8(B)).

Example 3 Super-Battery Cells Based on Graphene Materials (NGPs) fromNatural Graphite, Carbon Fibers, and Artificial Graphite and Based onCarbon Black (CB) and Treated CB

A wide variety of super-batteries have been prepared and tested in thepresent investigation. Oxidized NGP or graphene oxide (GO) was preparedwith a modified Hummers' method that involved exposing the startinggraphitic materials to a mixture of sulfuric acid, sodium nitrate, andpotassium permanganate at a ratio of 4:1:0.1 for 72 hours. The resultingGO was then thoroughly rinsed with water to obtain GO suspension, whichwas followed by two different routes of material preparation. One routeinvolved subjecting the GO suspension to ultrasonication to obtainisolated graphene oxide sheets suspended in water (N-type). The otherroute involved spray-drying GO suspension to obtain graphiteintercalation compound (GIC) or GO powder. The GIC or GO powder was thenthermally exfoliated at 1,050° C. for 45 seconds to obtain exfoliatedgraphite or graphite worms (G-type). Exfoliated graphite worms fromartificial graphite and carbon fibers were then subjected toultrasonication to separate or isolate oxidized graphene sheets. Carbonblack (CB) was subjected to a chemical treatment similar to the Hummers'method to open up nano-gates, enabling electrolyte access to theinterior (t-CB).

Each cathode, composed of 85% graphene, 5% Super-P (AB-based conductiveadditive), and 10% PTFE, was coated on Al foil. The thickness of theelectrode was typically around 150-200 μm, but an additional series ofsamples with thicknesses of approximately 80, 100, 150 μm was preparedto evaluate the effect of electrode size on the power and energydensities of the resulting supercapacitor-battery cells. Electrodes asthin as 20 μm were also made for comparison. The electrode was dried ina vacuum oven at 120° C. for 12 hours before use. The negative electrodewas Li metal foil. Coin-size cells were assembled in a glove box using1M LiPF₆/EC+DMC as electrolyte.

Example 4 Type-2 Super-Battery (Prelithiated Compound as a LithiumSource and Non-Functionalized Graphene as the Cathode Active Material)vs. Prior Art Lithium-Ion Capacitor (Prelithiated Graphite as an AnodeActive Material and Activated Carbon as the Cathode Active Material)

Natural graphite (supplied from Huadong Graphite Co., Qingdao, China)was made into an electrode and prelithiated by assembling the graphiteelectrode and a lithium foil into a half-cell configuration. Thegraphite electrode was “charged” with lithium up to an amount ofintercalated lithium corresponding to approximately 350 mAh/g ofgraphite weight using a voltage range of from 3.0 volts to 0 volts. Thishalf-cell was then disassembled and the prelithiated graphite electrodewas recovered. This prelithiated graphite was used as the anode activematerial, along with a sheet of porous separator, lithium salt-basedelectrolyte, and a non-functionalized graphene electrode as a cathodeactive material, to form a Type-2 super-battery. For comparison, acorresponding lithium-ion capacitor (LIC) was fabricated using activatedcarbon (AC, supplied from Ashbury Carbon Co.) as the cathode activematerial and a similar prelithiated graphite anode. The capacity of eachof the two cells was measured with galvanostatic experiments using anArbin SCTS electrochemical testing instrument. Cyclic voltammetry (CV)was conducted on a CHI 660 Instruments electrochemical workstation. Thegraphene-based super-battery (having an open-circuit voltage of 1.5volts) was operated in the voltage range of 1.5-4.5 volts, while theAC-based LIC (found to have an open-circuit voltage of 2.2 volts) wasoperated in the voltage range of 2.2-3.8 volts. Quite surprisingly, theLIC was not able to operate above 3.8 volts and, in contrast, thesuper-battery could easily reach 4.5 volts. The Ragone plots for thesetwo devices are shown in FIG. 9, which demonstrate the stunningdifference between the presently invented super-battery and the priorart lithium-ion capacitor.

In conclusion, the instant invention provides a revolutionary energystorage device that has the best features of both the supercapacitor andthe lithium ion battery. These partially surface-enabled, lithiumion-exchanging cells, with their materials and structures yet to beoptimized, are already capable of storing an energy density of typically80-160 Wh/kg_(cell), which is 30 times higher than that of conventionalelectric double layer (EDL) supercapacitors. The power density of 100kW/kg_(cell) is 10 times higher than that (10 kW/kg_(cell)) ofconventional EDL supercapacitors and 100 times higher than that (1kW/kg_(cell)) of conventional lithium-ion batteries. Thesesurface-mediated cells can be re-charged in seconds, as opposed to hoursfor conventional lithium ion batteries. This is truly a majorbreakthrough and revolutionary technology.

1. A lithium super-battery cell comprising: (a) A positive electrode(cathode) comprising a cathode active material having a surface area tocapture or store lithium thereon, wherein the cathode contains nofunctionalized material that has a functional group to capture a lithiumion; (b) A negative electrode (anode) being composed of an anode currentcollector and a lithium source implemented at the anode prior to a firstdischarge of the cell, wherein said lithium source is selected from alithium chip, lithium alloy chip, lithium foil, lithium alloy foil,lithium powder, lithium alloy powder, surface stabilized lithiumparticles, or a combination thereof; (c) A porous separator disposedbetween the two electrodes; and (d) A lithium-containing electrolyte inphysical contact with the two electrodes, wherein said cathode activematerial has a specific surface area of no less than 100 m²/g being indirect physical contact with said electrolyte to receive lithium ionstherefrom or to provide lithium ions thereto.
 2. The cell of claim 1,wherein said cell has an open-circuit voltage of at least 1.2 volts. 3.The cell of claim 1, wherein said device has an open-circuit voltage ofat least 1.5 volts.
 4. The cell of claim 1, wherein at least 90% of thelithium is stored on surfaces of said cathode active material, with saidlithium being in direct physical contact with said cathode surfaces,when the device is in a discharged state.
 5. The cell of claim 1,wherein the electrolyte is liquid electrolyte or gel electrolytecontaining a first amount of lithium ions.
 6. The cell of claim 1,wherein a charge or discharge operation of the cell does not involvelithium intercalation or solid state diffusion.
 7. The cell of claim 5,wherein an operation of said device involves an exchange of a secondamount of lithium ions between said cathode and said anode and saidsecond amount of lithium is greater than said first amount.
 8. The cellof claim 1, wherein said cell operates in a voltage range of from 1.5volts to 4.5 volts.
 9. The cell of claim 1, wherein said device operatesin a voltage range of from 1.5 volts to 4.0 volts.
 10. The cell of claim1, wherein said cell containing a liquid organic electrolyte operates ina voltage range above 3.8 volts.
 11. The cell of claim 1, wherein saidcathode has a specific surface area of no less than 500 m²/g that is indirect contact with said electrolyte.
 12. The cell of claim 1, whereinsaid cathode has a specific surface area of no less than 1,000 m²/g thatis in direct contact with said electrolyte.
 13. The cell of claim 1,wherein said cathode has a specific surface area of no less than 1,500m²/g that is in direct contact with said electrolyte.
 14. The cell ofclaim 1, wherein said cathode has a specific surface area of no lessthan 2,000 m²/g that is in direct contact with said electrolyte.
 15. Thecell of claim 1, wherein no more than 10% of the lithium is stored inthe bulk of said cathode active material when the device is in adischarged state.
 16. A lithium super-battery cell comprising: (a) Apositive electrode (cathode) of a non-functionalized graphene materialhaving no functional group to capture a lithium ion, wherein saidgraphene material is selected from a single-layer sheet or multi-layerplatelet of pristine graphene, graphene fluoride, hydrogenated graphene,nitrogenated graphene, boron-doped graphene, nitrogen-doped graphene,metal-doped graphene, reduced graphene oxide with less than 5% by weightof oxygen, or a combination thereof; (b) A negative electrode (anode)comprising an anode current collector; (c) A porous separator disposedbetween the two electrodes; (d) A lithium-containing electrolyte inphysical contact with the two electrodes, wherein said cathode activematerial has a specific surface area of no less than 100 m²/g being indirect physical contact with said electrolyte to receive lithium ionstherefrom or to provide lithium ions thereto; and (e) A lithium sourceimplemented in the anode or the cathode prior to a first discharge or afirst charge cycle of the cell, wherein said lithium source is selectedfrom a lithium intercalation compound, a lithiated compound, lithiatedtitanium dioxide, lithium titanate, lithium manganate, a lithiumtransition metal oxide, Li₄Ti₅O₁₂, or a combination thereof.
 17. Thecell of claim 16, wherein the lithium intercalation compound orlithiated compound is selected from the following groups of materials:(a) Lithiated silicon (Si), germanium (Ge), tin (Sn), lead (Pb),antimony (Sb), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti),cobalt (Co), nickel (Ni), manganese (Mn), cadmium (Cd), or a mixturethereof; (b) Lithiated alloys or intermetallic compounds of Si, Ge, Sn,Pb, Sb, Bi, Zn, Al, Ti, Co, Ni, Mn, Cd, or a mixture thereof; (c)Lithiated oxides, carbides, nitrides, sulfides, phosphides, selenides,tellurides, or antimonides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Fe, Ti,Co, Ni, Mn, Cd, or a mixture or composite thereof; (d) Lithiated saltsor hydroxides of Sn; (e) Prelithiated graphite or prelithiated carbonmaterial; or (f) A combination thereof.
 18. The cell of claim 1 whereinsaid cathode active material, containing no functional group, isselected from: (a) A porous disordered carbon material selected from asoft carbon, hard carbon, polymeric carbon or carbonized resin,meso-phase carbon, coke, carbonized pitch, carbon black, activatedcarbon, or partially graphitized carbon; (b) A graphene materialselected from a single-layer sheet or multi-layer platelet of graphene,graphene oxide, graphene fluoride, hydrogenated graphene, nitrogenatedgraphene, boron-doped graphene, nitrogen-doped graphene, or reducedgraphene oxide; (c) Exfoliated graphite; (d) Meso-porous carbon; (e) Acarbon nanotube selected from a single-walled carbon nanotube ormulti-walled carbon nanotube; (f) A carbon nano-fiber, metal nano-wire,metal oxide nano-wire or fiber, or conductive polymer nano-fiber, or (g)A combination thereof.
 19. The cell of claim 1 wherein said cathodeactive material is a graphene material containing no functional group.20. The cell of claim 18 wherein said disordered carbon material isformed of two phases with a first phase being graphite crystals orstacks of graphene planes and a second phase being non-crystallinecarbon, and wherein the first phase is dispersed in the second phase orbonded by the second phase.
 21. The cell of claim 1 wherein said cathodeactive material is a non-functionalized single-walled or multi-walledcarbon nanotube (CNT), fluorinated CNT, hydrogenated CNT, nitrogenatedCNT, boron-doped CNT, nitrogen-doped CNT, or doped CNT.
 22. The cell ofclaim 16, wherein the lithium source is in a thin film or fine particleform having a dimension less than 100 nm.
 23. The cell of claim 16,wherein the lithium source is in a thin film or fine particle formhaving a dimension less than 20 nm
 24. The cell of claim 1 wherein saidelectrolyte comprises a lithium salt-doped ionic liquid.
 25. The cell ofclaim 1 wherein said positive electrode has a thickness greater than 100μm.
 26. A method of operating the cell of claim 1, said method includingimplementing a lithium source at the anode and ionizing said lithiumsource to release lithium ions into said electrolyte during the firstdischarge cycle of said cell.
 27. A method of operating the cell ofclaim 1, said method including implementing a lithium source at thecathode and operating said lithium source to release lithium ions intosaid electrolyte during the first charge cycle of said cell.
 28. Amethod of operating the cell of claim 1, said method includingimplementing a lithium source at the anode, ionizing said lithium sourceto release lithium ions into said electrolyte during the first dischargecycle of said cell, and electrochemically driving said released lithiumions to said cathode where said released lithium ions are captured bysaid cathode active material surfaces.
 29. The method of claim 28,further comprising a step of releasing lithium ions from said cathodesurfaces during a re-charge cycle of said device, electrically drivingsaid released lithium ions to an anode current collector surface or saidlithium source using an external battery charging device.
 30. A methodof operating a lithium super-battery cell, said method including: (A)Providing a lithium super-battery cell comprising an anode, a lithiumsource, a porous separator, liquid or gel electrolyte, and a cathode,wherein the cathode has a non-functionalized material havinglithium-capturing surfaces and said cell has an open-circuit voltagefrom 0.5 volts to 2.0 volts; (B) Releasing lithium ions from saidlithium source into said electrolyte during the first discharge of saidcell; and (C) Exchanging lithium ions between the anode and thelithium-capturing surfaces of said cathode during a subsequent charge ordischarge in a cell operating in a voltage range of 1.5 volts and 4.5volts.
 31. The method of claim 30, wherein both the charge and dischargeof said cell do not involve lithium intercalation or solid statediffusion.
 32. The method of claim 30, wherein said lithium source is aprelithiated compound or lithium intercalation compound and said step(B) of releasing lithium ions from said lithium source occurs in a firstvoltage range, and wherein an operation of said cell occurs in a secondvoltage range different from the first voltage range.
 33. The method ofclaim 30, wherein said lithium source is a prelithiated graphite orprelithiated carbon material.
 34. The method of claim 32, wherein saidlithium source is a prelithiated graphite, prelithiated carbon material,lithiated titanium dioxide, lithium titanate, lithium manganate, alithium transition metal oxide, Li₄Ti₅O₁₂, or a combination thereof. 35.A method of operating a lithium super-battery cell, said methodincluding: (A) Providing a lithium super-battery cell comprising ananode, a lithium source, a porous separator, electrolyte having aninitial amount of lithium ions, and a cathode, wherein the cathode has amaterial having lithium-capturing surfaces in contact with saidelectrolyte; (B) Releasing lithium ions from said lithium source intosaid electrolyte during the first discharge of said cell; (C) Operatingsaid cathode to capture lithium ions from said electrolyte and storesaid captured lithium on cathode surfaces; and (D) Exchanging an amountof lithium ions, greater than said initial amount, between said anodeand the lithium-capturing surfaces of said cathode during a subsequentcharge or discharge operation.
 36. The method of claim 35 wherein saidcell has an open-circuit voltage of said cell is from 0.5 volts to 2.0volts.
 37. The method of claim 35 wherein said exchanging of lithiumions operates up to a voltage limit of no less than 4.0 volts.
 38. Themethod of claim 35 wherein said charge or discharge operation involvesno lithium intercalation.
 39. The method of claim 35, wherein saidcathode surfaces have a specific surface area greater than 100 m²/g. 40.The method of claim 35, wherein said cathode surfaces have a specificsurface area greater than 1,000 m²/g.
 41. The method of claim 35,wherein said cathode surfaces have a specific surface area greater than2,000 m²/g.